diff --git a/layout/README.md b/layout/README.md
index 1e76cb54..ce238f74 100644
--- a/layout/README.md
+++ b/layout/README.md
@@ -2,3 +2,19 @@
 
 this crate exposes several layout operators
 which are generic over `tek_engine::Engine`.
+
+* `Fill` makes the content's dimension equal to the container's.
+* `Fixed` assigns a fixed dimension to its content.
+* `Shrink` reduces the dimension of the content
+* `Expand` increases the dimension of the content
+* `Min` enforces minimum dimension for the content
+* `Max` enforces maximum dimension for the content
+* `Push` moves the content in the positive direction
+* `Pull` moves the content in the negative direction
+* `Margin` grows each dimension from both ends
+* `Padding` shrinks each dimension from both ends
+* `Align` pins the content along an axis of the container
+* `When` renders a content conditionally
+* `Either` alternates between two contents
+* `Map` transforms each content
+* `Reduce` transforms all contents into one
diff --git a/layout/src/align.rs b/layout/src/align.rs
new file mode 100644
index 00000000..403d41e5
--- /dev/null
+++ b/layout/src/align.rs
@@ -0,0 +1,76 @@
+use crate::*;
+
+#[derive(Default, Debug, Copy, Clone)]
+pub enum Alignment { #[default] Center, X, Y, NW, N, NE, E, SE, S, SW, W }
+
+pub struct Align<E: Engine, T: Content<E>>(Alignment, T, PhantomData<E>);
+
+impl<E: Engine, T: Content<E>> Align<E, T> {
+    pub fn c  (w: T) -> Self { Self(Alignment::Center, w, Default::default()) }
+    pub fn x  (w: T) -> Self { Self(Alignment::X, w, Default::default())      }
+    pub fn y  (w: T) -> Self { Self(Alignment::Y, w, Default::default())      }
+    pub fn n  (w: T) -> Self { Self(Alignment::N, w, Default::default())      }
+    pub fn s  (w: T) -> Self { Self(Alignment::S, w, Default::default())      }
+    pub fn e  (w: T) -> Self { Self(Alignment::E, w, Default::default())      }
+    pub fn w  (w: T) -> Self { Self(Alignment::W, w, Default::default())      }
+    pub fn nw (w: T) -> Self { Self(Alignment::NW, w, Default::default())     }
+    pub fn sw (w: T) -> Self { Self(Alignment::SW, w, Default::default())     }
+    pub fn ne (w: T) -> Self { Self(Alignment::NE, w, Default::default())     }
+    pub fn se (w: T) -> Self { Self(Alignment::SE, w, Default::default())     }
+}
+
+impl<E: Engine, T: Content<E>> Content<E> for Align<E, T> {
+    fn area (&self, outer: E::Area) -> E::Area {
+        align_areas(self.0, outer.xywh(), Content::area(&self.content(), outer).xywh()).into()
+    }
+    fn render (&self, render: &mut E::Output) {
+        render.place(self.area(render.area()), &self.content())
+    }
+}
+
+pub fn align_areas<N: Coordinate>(alignment: Alignment, on: [N;4], it: [N;4]) -> [N;4] {
+    let [cfx, cfy] = on.center();
+    let [cmx, cmy] = it.center();
+    let center     = |cf, cm, m: N|if cf >= cm { m + (cf - cm) } else { m.minus(cm - cf) };
+    let center_x   = center(cfx, cmx, it.x());
+    let center_y   = center(cfy, cmy, it.y());
+    let east_x     = on.x() + on.w().minus(it.w());
+    let south_y    = on.y() + on.h().minus(it.h());
+    match alignment {
+        Alignment::Center => [center_x, center_y, it.w(), it.h()],
+        Alignment::X      => [center_x, it.y(),   it.w(), it.h()],
+        Alignment::Y      => [it.x(),   center_y, it.w(), it.h()],
+
+        Alignment::NW     => [on.x(),   on.y(),   it.w(), it.h()],
+        Alignment::N      => [center_x, on.y(),   it.w(), it.h()],
+        Alignment::NE     => [east_x,   on.y(),   it.w(), it.h()],
+        Alignment::E      => [east_x,   center_y, it.w(), it.h()],
+        Alignment::SE     => [east_x,   south_y,  it.w(), it.h()],
+        Alignment::S      => [center_x, south_y,  it.w(), it.h()],
+        Alignment::SW     => [on.x(),   south_y,  it.w(), it.h()],
+        Alignment::W      => [on.x(),   center_y, it.w(), it.h()],
+    }
+}
+
+//fn align<E: Engine, T: Content<E>, N: Coordinate, R: Area<N> + From<[N;4]>> (align: &Align<E, T>, outer: R, content: R) -> Option<R> {
+    //if outer.w() < content.w() || outer.h() < content.h() {
+        //None
+    //} else {
+        //let [ox, oy, ow, oh] = outer.xywh();
+        //let [ix, iy, iw, ih] = content.xywh();
+        //Some(match align {
+            //Align::Center(_) => [ox + (ow - iw) / 2.into(), oy + (oh - ih) / 2.into(), iw, ih,].into(),
+            //Align::X(_)  => [ox + (ow - iw) / 2.into(), iy, iw, ih,].into(),
+            //Align::Y(_)  => [ix, oy + (oh - ih) / 2.into(), iw, ih,].into(),
+            //Align::NW(_) => [ox, oy, iw, ih,].into(),
+            //Align::N(_)  => [ox + (ow - iw) / 2.into(), oy, iw, ih,].into(),
+            //Align::NE(_) => [ox + ow - iw, oy, iw, ih,].into(),
+            //Align::W(_)  => [ox, oy + (oh - ih) / 2.into(), iw, ih,].into(),
+            //Align::E(_)  => [ox + ow - iw, oy + (oh - ih) / 2.into(), iw, ih,].into(),
+            //Align::SW(_) => [ox, oy + oh - ih, iw, ih,].into(),
+            //Align::S(_)  => [ox + (ow - iw) / 2.into(), oy + oh - ih, iw, ih,].into(),
+            //Align::SE(_) => [ox + ow - iw, oy + oh - ih, iw, ih,].into(),
+            //_ => unreachable!()
+        //})
+    //}
+//}
diff --git a/layout/src/bsp.rs b/layout/src/bsp.rs
new file mode 100644
index 00000000..bf2258a6
--- /dev/null
+++ b/layout/src/bsp.rs
@@ -0,0 +1,144 @@
+use crate::*;
+
+/// Renders multiple things on top of each other,
+#[macro_export] macro_rules! lay {
+    ($($expr:expr),* $(,)?) => {{
+        let bsp = ();
+        $(let bsp = Bsp::b(bsp, $expr);)*;
+        bsp
+    }}
+}
+
+/// Stack southward.
+#[macro_export] macro_rules! col {
+    ($($expr:expr),* $(,)?) => {{
+        let bsp = ();
+        $(let bsp = Bsp::s(bsp, $expr);)*;
+        bsp
+    }};
+}
+
+/// Stack northward.
+#[macro_export] macro_rules! col_up {
+    ($($expr:expr),* $(,)?) => {{
+        let bsp = ();
+        $(let bsp = Bsp::n(bsp, $expr);)*;
+        bsp
+    }}
+}
+
+/// Stack eastward.
+#[macro_export] macro_rules! row {
+    ($($expr:expr),* $(,)?) => {{
+        let bsp = ();
+        $(let bsp = Bsp::e(bsp, $expr);)*;
+        bsp
+    }};
+}
+
+pub enum Bsp<E: Engine, X: Content<E>, Y: Content<E>> {
+    /// X is north of Y
+    North(Option<f64>, Option<X>, Option<Y>),
+    /// X is south of Y
+    South(Option<f64>, Option<X>, Option<Y>),
+    /// X is east of Y
+    East(Option<f64>, Option<X>, Option<Y>),
+    /// X is west of Y
+    West(Option<f64>, Option<X>, Option<Y>),
+    /// X is above Y
+    Above(Option<X>, Option<Y>),
+    /// X is below Y
+    Below(Option<X>, Option<Y>),
+    /// Should be avoided.
+    Null(PhantomData<E>),
+}
+
+impl<E: Engine, X: Content<E>, Y: Content<E>> Bsp<E, X, Y> {
+    pub fn n (x: X, y: Y) -> Self { Self::North(None, Some(x), Some(y)) }
+    pub fn s (x: X, y: Y) -> Self { Self::South(None, Some(x), Some(y)) }
+    pub fn e (x: X, y: Y) -> Self { Self::East(None, Some(x), Some(y)) }
+    pub fn w (x: X, y: Y) -> Self { Self::West(None, Some(x), Some(y)) }
+    pub fn a (x: X, y: Y) -> Self { Self::Above(Some(x), Some(y)) }
+    pub fn b (x: X, y: Y) -> Self { Self::Below(Some(x), Some(y)) }
+}
+
+impl<E: Engine, X: Content<E>, Y: Content<E>> Default for Bsp<E, X, Y> {
+    fn default () -> Self {
+        Self::Null(Default::default())
+    }
+}
+
+impl<E: Engine, X: Content<E>, Y: Content<E>> Content<E> for Bsp<E, X, Y> {
+    fn area (&self, outer: E::Area) -> E::Area {
+        match self {
+            Self::Null(_) => [0.into(), 0.into(), 0.into(), 0.into()].into(),
+            Self::North(_, a, b) => {
+                let a = a.area(outer);
+                let b = b.area(North.split_fixed(outer, a.y() + a.h()).1.into());
+                [a.x().min(b.x()), a.y().min(b.y()), a.w().max(b.w()), a.h() + b.h()].into()
+            }
+            Self::South(_, a, b) => {
+                let a = a.area(outer);
+                let b = b.area(South.split_fixed(outer, a.y() + a.h()).1.into());
+                [a.x().min(b.x()), a.y().min(b.y()), a.w().max(b.w()), a.h() + b.h()].into()
+            },
+            Self::East(_, a, b) => {
+                let a = a.area(outer);
+                let b = b.area(East.split_fixed(outer, a.x() + a.w()).1.into());
+                [a.x().min(b.x()), a.y().min(b.y()), a.w() + b.w(), a.h().max(b.h())].into()
+            },
+            Self::West(_, a, b) => {
+                let a = a.area(outer);
+                let b = b.area(West.split_fixed(outer, a.x() + a.w()).1.into());
+                [a.x().min(b.x()), a.y().min(b.y()), a.w() + b.w(), a.h().max(b.h())].into()
+            },
+            Self::Above(a, b) | Self::Below(a, b) => {
+                let a = a.area(outer);
+                let b = b.area(outer);
+                [a.x().min(b.x()), a.y().min(b.y()), a.w().max(b.w()), a.h().max(b.h())].into()
+            }
+        }
+    }
+    fn render (&self, to: &mut E::Output) {
+        let area = to.area().clone();
+        match self {
+            Self::North(_, a, b) => {
+                let area_a = a.area(area);
+                let area_b = b.area(North.split_fixed(area, area_a.y() + area_a.h()).1.into());
+                to.place(area_a, a);
+                to.place(area_b, b);
+            },
+            Self::South(_, a, b) => {
+                let area_a = a.area(area).clone();
+                let area_b = b.area(South.split_fixed(area, area_a.y() + area_a.h()).1.into()).clone();
+                to.place(area_a, a);
+                to.place(area_b, b);
+            },
+            Self::East(_, a, b) => {
+                let area_a = a.area(area);
+                let area_b = b.area(East.split_fixed(area, area_a.x() + area_a.w()).1.into());
+                to.place(area_a, a);
+                to.place(area_b, b);
+            },
+            Self::West(_, a, b) => {
+                let area_a = a.area(area);
+                let area_b = b.area(West.split_fixed(area, area_a.x() + area_a.w()).1.into());
+                to.place(area_a, a);
+                to.place(area_b, b);
+            },
+            Self::Above(a, b) => {
+                let area_a = a.area(area);
+                let area_b = b.area(area);
+                to.place(area_b, b);
+                to.place(area_a, a);
+            },
+            Self::Below(a, b) => {
+                let area_a = a.area(area);
+                let area_b = b.area(area);
+                to.place(area_a, a);
+                to.place(area_b, b);
+            },
+            Self::Null(_) => {}
+        }
+    }
+}
diff --git a/layout/src/collection.rs b/layout/src/collection.rs
index 5d48b6d3..5559afea 100644
--- a/layout/src/collection.rs
+++ b/layout/src/collection.rs
@@ -1,88 +1,14 @@
 //! Groupings of elements.
-
-//mod split;  pub use self::split::*;
-//mod stack;  pub use self::stack::*;
-
 use crate::*;
 
-use std::sync::RwLock;
+/// A function or closure that emits renderables.
+pub trait Collector<E: Engine>: Send + Sync + Fn(&mut dyn FnMut(&dyn Render<E>)) {}
 
-impl<E: Engine> Layout<E> for E {}
+/// Any function or closure that emits renderables for the given engine matches [CollectCallback].
+impl<E, F> Collector<E> for F
+where E: Engine, F: Send + Sync + Fn(&mut dyn FnMut(&dyn Render<E>)) {}
 
-pub trait Layout<E: Engine> {
-    /// Content `item` when `cond` is true.
-    fn when <A: Content<E>> (cond: bool, item: A) -> When<E, A> {
-        When(cond, item, Default::default())
-    }
-    /// Content `item` if `cond` is true, otherwise render `other`.
-    fn either <A: Content<E>, B: Content<E>> (cond: bool, a: A, b: B)
-        -> Either<E, A, B>
-    {
-        Either(cond, a, b, Default::default())
-    }
-    /// Maps an [Option<T>] through a callback `F`
-    fn opt <A, F: Fn(A)->R, R: Content<E>> (option: Option<A>, cb: F)
-        -> Opt<E, A, F, R>
-    {
-        Opt(option, cb, Default::default())
-    }
-    fn map <T, I, R, F>(iterator: I, callback: F) -> Map<E, T, I, R, F> where
-        E: Engine,
-        I: Iterator<Item = T> + Send + Sync,
-        R: Content<E>,
-        F: Fn(T, usize)->R + Send + Sync
-    {
-        Map(Default::default(), RwLock::new(iterator), callback)
-    }
-    //pub fn reduce <E, T, I, R, F>(iterator: I, callback: F) -> Reduce<E, T, I, R, F> where
-        //E: Engine,
-        //I: Iterator<Item = T> + Send + Sync,
-        //R: Content<E>,
-        //F: Fn(R, T, usize) -> R + Send + Sync
-    //{
-        //Reduce(Default::default(), iterator, callback)
-    //}
-}
-
-pub struct Opt<E: Engine, A, F: Fn(A)->R, R: Content<E>>(Option<A>, F, PhantomData<E>);
-
-/// Contents `self.1` when `self.0` is true.
-pub struct When<E: Engine, A>(bool, A, PhantomData<E>);
-
-impl<E: Engine, A: Content<E>> Content<E> for When<E, A> {
-    fn area (&self, to: E::Area) -> E::Area {
-        let Self(cond, item, ..) = self;
-        let mut area = E::Area::zero();
-        if *cond {
-            let item_area = item.area(to);
-            area[0] = item_area.x();
-            area[1] = item_area.y();
-            area[2] = item_area.w();
-            area[3] = item_area.h();
-        }
-        area.into()
-    }
-    fn render (&self, to: &mut E::Output) {
-        let Self(cond, item, ..) = self;
-        if *cond { item.render(to) }
-    }
-}
-
-/// Contents `self.1` when `self.0` is true, otherwise renders `self.2`
-pub struct Either<E: Engine, A, B>(bool, A, B, PhantomData<E>);
-
-impl<E: Engine, A: Content<E>, B: Content<E>> Content<E> for Either<E, A, B> {
-    fn area (&self, to: E::Area) -> E::Area {
-        let Self(cond, a, b, ..) = self;
-        if *cond { a.area(to) } else { b.area(to) }
-    }
-    fn render (&self, to: &mut E::Output) {
-        let Self(cond, a, b, ..) = self;
-        if *cond { a.render(to) } else { b.render(to) }
-    }
-}
-
-trait Render<E: Engine> {
+pub trait Render<E: Engine> {
     fn area (&self, to: E::Area) -> E::Area;
     fn render (&self, to: &mut E::Output);
 }
@@ -95,55 +21,3 @@ impl<E: Engine, C: Content<E>> Render<E> for C {
         Content::render(self, to)
     }
 }
-
-/// A function or closure that emits renderables.
-pub trait Collector<E: Engine>: Send + Sync + Fn(&mut dyn FnMut(&dyn Render<E>)) {}
-
-/// Any function or closure that emits renderables for the given engine matches [CollectCallback].
-impl<E, F> Collector<E> for F
-where E: Engine, F: Send + Sync + Fn(&mut dyn FnMut(&dyn Render<E>)) {}
-
-/// Rendering of iterable collections, one-to-one and many-to one.
-pub struct Coll;
-
-impl Coll {
-}
-
-pub struct Map<E, T, I, R, F>(PhantomData<E>, RwLock<I>, F) where
-    E: Engine,
-    I: Iterator<Item = T> + Send + Sync,
-    R: Content<E>,
-    F: Fn(T, usize)->R + Send + Sync;
-
-impl<E, T, I, R, F> Content<E> for Map<E, T, I, R, F> where
-    E: Engine,
-    I: Iterator<Item = T> + Send + Sync,
-    R: Content<E>,
-    F: Fn(T, usize)->R + Send + Sync
-{
-    fn render (&self, to: &mut E::Output) {
-        let mut index = 0;
-        for item in &mut*self.1.write().unwrap() {
-            (self.2)(item, index).render(to);
-            index += 1;
-        }
-    }
-}
-
-/*
-pub struct Reduce<E, T, I, R, F>(PhantomData<(E, R)>, I, F) where
-    E: Engine,
-    I: Iterator<Item = T> + Send + Sync,
-    R: Content<E>,
-    F: Fn(R, T, usize) -> R + Send + Sync;
-impl<E, T, I, R, F> Content<E> for Reduce<E, T, I, R, F> where
-    E: Engine,
-    I: Iterator<Item = T> + Send + Sync,
-    R: Content<E>,
-    F: Fn(R, T, usize) -> R + Send + Sync
-{
-    fn render (&self, to: &mut E::Output) {
-        todo!()
-    }
-}
-*/
diff --git a/layout/src/collection/split.rs b/layout/src/collection/split.rs
deleted file mode 100644
index cff769ed..00000000
--- a/layout/src/collection/split.rs
+++ /dev/null
@@ -1,36 +0,0 @@
-use crate::*;
-
-/// A binary split with fixed proportion
-pub struct Split<E, A, B>(pub bool, pub Direction, pub E::Unit, A, B, PhantomData<E>)
-where E: Engine, A: Content<E>, B: Content<E>;
-
-impl<E: Engine, A: Content<E>, B: Content<E>> Split<E, A, B> {
-    #[inline] pub fn new (flip: bool, direction: Direction, proportion: E::Unit, a: A, b: B) -> Self {
-        Self(flip, direction, proportion, a, b, Default::default())
-    }
-    #[inline] pub fn n (flip: bool, proportion: E::Unit, a: A, b: B) -> Self {
-        Self::new(flip, North, proportion, a, b)
-    }
-    #[inline] pub fn s (flip: bool, proportion: E::Unit, a: A, b: B) -> Self {
-        Self::new(flip, South, proportion, a, b)
-    }
-    #[inline] pub fn e (flip: bool, proportion: E::Unit, a: A, b: B) -> Self {
-        Self::new(flip, West, proportion, a, b)
-    }
-    #[inline] pub fn w (flip: bool, proportion: E::Unit, a: A, b: B) -> Self {
-        Self::new(flip, East, proportion, a, b)
-    }
-}
-
-impl<E: Engine, A: Content<E>, B: Content<E>> Content<E> for Split<E, A, B> {
-    fn render (&self, to: &mut E::Output) {
-        let (a, b) = self.1.split_fixed(to.area(), self.2);
-        if self.0 {
-            to.place(a.into(), &self.4);
-            to.place(b.into(), &self.3);
-        } else {
-            to.place(a.into(), &self.3);
-            to.place(b.into(), &self.4);
-        }
-    }
-}
diff --git a/layout/src/collection/stack.rs b/layout/src/collection/stack.rs
deleted file mode 100644
index c178bc97..00000000
--- a/layout/src/collection/stack.rs
+++ /dev/null
@@ -1,117 +0,0 @@
-use crate::*;
-
-pub struct Stack<E: Engine, F: Collector<E>>(pub F, pub Direction, PhantomData<E>);
-
-impl<E: Engine, F: Collector<E>> Stack<E, F> {
-    #[inline] pub fn new (direction: Direction, build: F) -> Self {
-        Self(build, direction, Default::default())
-    }
-    #[inline] pub fn right (build: F) -> Self {
-        Self::new(East, build)
-    }
-    #[inline] pub fn down (build: F) -> Self {
-        Self::new(South, build)
-    }
-    #[inline] pub fn up (build: F) -> Self {
-        Self::new(North, build)
-    }
-}
-
-//#[macro_export] macro_rules! col {
-    //([$($expr:expr),* $(,)?]) => {
-        //Stack::down(move|add|{ $(add(&$expr)?;)* Ok(()) })
-    //};
-    //(![$($expr:expr),* $(,)?]) => {
-        //Stack::down(|add|{ $(add(&$expr)?;)* Ok(()) })
-    //};
-    //($expr:expr) => {
-        //Stack::down($expr)
-    //};
-    //($pat:pat in $collection:expr => $item:expr) => {
-        //Stack::down(move|add|{ for $pat in $collection { add(&$item)?; } Ok(()) })
-    //};
-//}
-
-//#[macro_export] macro_rules! col_up {
-    //([$($expr:expr),* $(,)?]) => {
-        //Stack::up(move|add|{ $(add(&$expr)?;)* Ok(()) })
-    //};
-    //(![$($expr:expr),* $(,)?]) => {
-        //Stack::up(|add|{ $(add(&$expr)?;)* Ok(()) })
-    //};
-    //($expr:expr) => {
-        //Stack::up(expr)
-    //};
-    //($pat:pat in $collection:expr => $item:expr) => {
-        //Stack::up(move |add|{ for $pat in $collection { add(&$item)?; } Ok(()) })
-    //};
-//}
-
-//#[macro_export] macro_rules! row {
-    //([$($expr:expr),* $(,)?]) => {
-        //Stack::right(move|add|{ $(add(&$expr)?;)* Ok(()) })
-    //};
-    //(![$($expr:expr),* $(,)?]) => {
-        //Stack::right(|add|{ $(add(&$expr)?;)* Ok(()) })
-    //};
-    //($expr:expr) => {
-        //Stack::right($expr)
-    //};
-    //($pat:pat in $collection:expr => $item:expr) => {
-        //Stack::right(move|add|{ for $pat in $collection { add(&$item)?; } Ok(()) })
-    //};
-//}
-
-//impl<E: Engine, F: Collector<E>> Content<E> for Stack<E, F> {
-    //fn render (&self, to: &mut E::Output) {
-        //let area = to.area();
-        //let mut w = 0.into();
-        //let mut h = 0.into();
-        //match self.1 {
-            //South => {
-                //(self.0)(&mut |item| {
-                    //if h < area.h() {
-                        //let item = Max::y(area.h() - h, Push::y(h, item));
-                        //let show = item.min_size(area.wh().into())?.map(|s|s.wh());
-                        //if let Some([width, height]) = show {
-                            //item.render(to)?;
-                            //h = h + height;
-                            //if width > w { w = width }
-                        //};
-                    //}
-                    //Ok(())
-                //})?;
-            //},
-            //East => {
-                //(self.0)(&mut |item| {
-                    //if w < area.w() {
-                        //let item = Max::x(area.w() - w, Push::x(w, item));
-                        //let show = item.min_size(area.wh().into())?.map(|s|s.wh());
-                        //if let Some([width, height]) = show {
-                            //item.render(to)?;
-                            //w = width + w;
-                            //if height > h { h = height }
-                        //};
-                    //}
-                    //Ok(())
-                //})?;
-            //},
-            //North => {
-                //(self.0)(&mut |item| {
-                    //if h < area.h() {
-                        //let show = item.min_size([area.w(), area.h().minus(h)].into())?.map(|s|s.wh());
-                        //if let Some([width, height]) = show {
-                            //Shrink::y(height, Push::y(area.h() - height, item))
-                                //.render(to)?;
-                            //h = h + height;
-                            //if width > w { w = width }
-                        //};
-                    //}
-                    //Ok(())
-                //})?;
-            //},
-            //_ => todo!()
-        //};
-        //Ok(())
-    //}
-//}
diff --git a/layout/src/direction.rs b/layout/src/direction.rs
index 13609213..8c189e3f 100644
--- a/layout/src/direction.rs
+++ b/layout/src/direction.rs
@@ -50,146 +50,3 @@ impl Direction {
         }
     }
 }
-
-/// Renders multiple things on top of each other,
-#[macro_export] macro_rules! lay {
-    ($($expr:expr),* $(,)?) => {{
-        let bsp = ();
-        $(let bsp = Bsp::b(bsp, $expr);)*;
-        bsp
-    }}
-}
-
-/// Stack southward.
-#[macro_export] macro_rules! col {
-    ($($expr:expr),* $(,)?) => {{
-        let bsp = ();
-        $(let bsp = Bsp::s(bsp, $expr);)*;
-        bsp
-    }};
-}
-
-/// Stack northward.
-#[macro_export] macro_rules! col_up {
-    ($($expr:expr),* $(,)?) => {{
-        let bsp = ();
-        $(let bsp = Bsp::n(bsp, $expr);)*;
-        bsp
-    }}
-}
-
-/// Stack eastward.
-#[macro_export] macro_rules! row {
-    ($($expr:expr),* $(,)?) => {{
-        let bsp = ();
-        $(let bsp = Bsp::e(bsp, $expr);)*;
-        bsp
-    }};
-}
-
-pub enum Bsp<E: Engine, X: Content<E>, Y: Content<E>> {
-    /// X is north of Y
-    North(Option<f64>, Option<X>, Option<Y>),
-    /// X is south of Y
-    South(Option<f64>, Option<X>, Option<Y>),
-    /// X is east of Y
-    East(Option<f64>, Option<X>, Option<Y>),
-    /// X is west of Y
-    West(Option<f64>, Option<X>, Option<Y>),
-    /// X is above Y
-    Above(Option<X>, Option<Y>),
-    /// X is below Y
-    Below(Option<X>, Option<Y>),
-    /// Should be avoided.
-    Null(PhantomData<E>),
-}
-
-impl<E: Engine, X: Content<E>, Y: Content<E>> Bsp<E, X, Y> {
-    pub fn n (x: X, y: Y) -> Self { Self::North(None, Some(x), Some(y)) }
-    pub fn s (x: X, y: Y) -> Self { Self::South(None, Some(x), Some(y)) }
-    pub fn e (x: X, y: Y) -> Self { Self::East(None, Some(x), Some(y)) }
-    pub fn w (x: X, y: Y) -> Self { Self::West(None, Some(x), Some(y)) }
-    pub fn a (x: X, y: Y) -> Self { Self::Above(Some(x), Some(y)) }
-    pub fn b (x: X, y: Y) -> Self { Self::Below(Some(x), Some(y)) }
-}
-
-impl<E: Engine, X: Content<E>, Y: Content<E>> Default for Bsp<E, X, Y> {
-    fn default () -> Self {
-        Self::Null(Default::default())
-    }
-}
-
-impl<E: Engine, X: Content<E>, Y: Content<E>> Content<E> for Bsp<E, X, Y> {
-    fn area (&self, outer: E::Area) -> E::Area {
-        match self {
-            Self::Null(_) => [0.into(), 0.into(), 0.into(), 0.into()].into(),
-            Self::North(_, a, b) => {
-                let a = a.area(outer);
-                let b = b.area(North.split_fixed(outer, a.y() + a.h()).1.into());
-                [a.x().min(b.x()), a.y().min(b.y()), a.w().max(b.w()), a.h() + b.h()].into()
-            }
-            Self::South(_, a, b) => {
-                let a = a.area(outer);
-                let b = b.area(South.split_fixed(outer, a.y() + a.h()).1.into());
-                [a.x().min(b.x()), a.y().min(b.y()), a.w().max(b.w()), a.h() + b.h()].into()
-            },
-            Self::East(_, a, b) => {
-                let a = a.area(outer);
-                let b = b.area(East.split_fixed(outer, a.x() + a.w()).1.into());
-                [a.x().min(b.x()), a.y().min(b.y()), a.w() + b.w(), a.h().max(b.h())].into()
-            },
-            Self::West(_, a, b) => {
-                let a = a.area(outer);
-                let b = b.area(West.split_fixed(outer, a.x() + a.w()).1.into());
-                [a.x().min(b.x()), a.y().min(b.y()), a.w() + b.w(), a.h().max(b.h())].into()
-            },
-            Self::Above(a, b) | Self::Below(a, b) => {
-                let a = a.area(outer);
-                let b = b.area(outer);
-                [a.x().min(b.x()), a.y().min(b.y()), a.w().max(b.w()), a.h().max(b.h())].into()
-            }
-        }
-    }
-    fn render (&self, to: &mut E::Output) {
-        let area = to.area().clone();
-        match self {
-            Self::North(_, a, b) => {
-                let area_a = a.area(area);
-                let area_b = b.area(North.split_fixed(area, area_a.y() + area_a.h()).1.into());
-                to.place(area_a, a);
-                to.place(area_b, b);
-            },
-            Self::South(_, a, b) => {
-                let area_a = a.area(area).clone();
-                let area_b = b.area(South.split_fixed(area, area_a.y() + area_a.h()).1.into()).clone();
-                to.place(area_a, a);
-                to.place(area_b, b);
-            },
-            Self::East(_, a, b) => {
-                let area_a = a.area(area);
-                let area_b = b.area(East.split_fixed(area, area_a.x() + area_a.w()).1.into());
-                to.place(area_a, a);
-                to.place(area_b, b);
-            },
-            Self::West(_, a, b) => {
-                let area_a = a.area(area);
-                let area_b = b.area(West.split_fixed(area, area_a.x() + area_a.w()).1.into());
-                to.place(area_a, a);
-                to.place(area_b, b);
-            },
-            Self::Above(a, b) => {
-                let area_a = a.area(area);
-                let area_b = b.area(area);
-                to.place(area_b, b);
-                to.place(area_a, a);
-            },
-            Self::Below(a, b) => {
-                let area_a = a.area(area);
-                let area_b = b.area(area);
-                to.place(area_a, a);
-                to.place(area_b, b);
-            },
-            Self::Null(_) => {}
-        }
-    }
-}
diff --git a/layout/src/lib.rs b/layout/src/lib.rs
index e8bdb134..bead884a 100644
--- a/layout/src/lib.rs
+++ b/layout/src/lib.rs
@@ -1,7 +1,12 @@
-mod collection; pub use self::collection::*;
-mod direction;  pub use self::direction::*;
-mod measure;    pub use self::measure::*;
-mod transform;  pub use self::transform::*;
+//mod collection; pub use self::collection::*;
+
+mod align;              pub use self::align::*;
+mod bsp;                pub use self::bsp::*;
+mod direction;          pub use self::direction::*;
+mod measure;            pub use self::measure::*;
+mod ops;                pub use self::ops::*;
+mod transform_xy;       pub use self::transform_xy::*;
+mod transform_xy_unit;  pub use self::transform_xy_unit::*;
 
 pub use ::tek_engine;
 pub(crate) use ::tek_engine::*;
diff --git a/layout/src/ops.rs b/layout/src/ops.rs
new file mode 100644
index 00000000..baadfab9
--- /dev/null
+++ b/layout/src/ops.rs
@@ -0,0 +1,117 @@
+use crate::*;
+
+use std::sync::RwLock;
+
+impl<E: Engine> Layout<E> for E {}
+
+pub trait Layout<E: Engine> {
+    /// Content `item` when `cond` is true.
+    fn when <A: Content<E>> (cond: bool, item: A) -> When<E, A> {
+        When(cond, item, Default::default())
+    }
+    /// Content `item` if `cond` is true, otherwise render `other`.
+    fn either <A: Content<E>, B: Content<E>> (cond: bool, a: A, b: B)
+        -> Either<E, A, B>
+    {
+        Either(cond, a, b, Default::default())
+    }
+    /// Maps an [Option<T>] through a callback `F`
+    fn opt <A, F: Fn(A)->R, R: Content<E>> (option: Option<A>, cb: F)
+        -> Opt<E, A, F, R>
+    {
+        Opt(option, cb, Default::default())
+    }
+    fn map <T, I, R, F>(iterator: I, callback: F) -> Map<E, T, I, R, F> where
+        E: Engine,
+        I: Iterator<Item = T> + Send + Sync,
+        R: Content<E>,
+        F: Fn(T, usize)->R + Send + Sync
+    {
+        Map(Default::default(), RwLock::new(iterator), callback)
+    }
+    //pub fn reduce <E, T, I, R, F>(iterator: I, callback: F) -> Reduce<E, T, I, R, F> where
+        //E: Engine,
+        //I: Iterator<Item = T> + Send + Sync,
+        //R: Content<E>,
+        //F: Fn(R, T, usize) -> R + Send + Sync
+    //{
+        //Reduce(Default::default(), iterator, callback)
+    //}
+}
+
+pub struct Opt<E: Engine, A, F: Fn(A)->R, R: Content<E>>(Option<A>, F, PhantomData<E>);
+
+/// Contents `self.1` when `self.0` is true.
+pub struct When<E: Engine, A>(bool, A, PhantomData<E>);
+
+impl<E: Engine, A: Content<E>> Content<E> for When<E, A> {
+    fn area (&self, to: E::Area) -> E::Area {
+        let Self(cond, item, ..) = self;
+        let mut area = E::Area::zero();
+        if *cond {
+            let item_area = item.area(to);
+            area[0] = item_area.x();
+            area[1] = item_area.y();
+            area[2] = item_area.w();
+            area[3] = item_area.h();
+        }
+        area.into()
+    }
+    fn render (&self, to: &mut E::Output) {
+        let Self(cond, item, ..) = self;
+        if *cond { item.render(to) }
+    }
+}
+
+/// Contents `self.1` when `self.0` is true, otherwise renders `self.2`
+pub struct Either<E: Engine, A, B>(bool, A, B, PhantomData<E>);
+
+impl<E: Engine, A: Content<E>, B: Content<E>> Content<E> for Either<E, A, B> {
+    fn area (&self, to: E::Area) -> E::Area {
+        let Self(cond, a, b, ..) = self;
+        if *cond { a.area(to) } else { b.area(to) }
+    }
+    fn render (&self, to: &mut E::Output) {
+        let Self(cond, a, b, ..) = self;
+        if *cond { a.render(to) } else { b.render(to) }
+    }
+}
+
+pub struct Map<E, T, I, R, F>(PhantomData<E>, RwLock<I>, F) where
+    E: Engine,
+    I: Iterator<Item = T> + Send + Sync,
+    R: Content<E>,
+    F: Fn(T, usize)->R + Send + Sync;
+
+impl<E, T, I, R, F> Content<E> for Map<E, T, I, R, F> where
+    E: Engine,
+    I: Iterator<Item = T> + Send + Sync,
+    R: Content<E>,
+    F: Fn(T, usize)->R + Send + Sync
+{
+    fn render (&self, to: &mut E::Output) {
+        let mut index = 0;
+        for item in &mut*self.1.write().unwrap() {
+            (self.2)(item, index).render(to);
+            index += 1;
+        }
+    }
+}
+
+/*
+pub struct Reduce<E, T, I, R, F>(PhantomData<(E, R)>, I, F) where
+    E: Engine,
+    I: Iterator<Item = T> + Send + Sync,
+    R: Content<E>,
+    F: Fn(R, T, usize) -> R + Send + Sync;
+impl<E, T, I, R, F> Content<E> for Reduce<E, T, I, R, F> where
+    E: Engine,
+    I: Iterator<Item = T> + Send + Sync,
+    R: Content<E>,
+    F: Fn(R, T, usize) -> R + Send + Sync
+{
+    fn render (&self, to: &mut E::Output) {
+        todo!()
+    }
+}
+*/
diff --git a/layout/src/transform.rs b/layout/src/transform.rs
deleted file mode 100644
index c21345e2..00000000
--- a/layout/src/transform.rs
+++ /dev/null
@@ -1,227 +0,0 @@
-use crate::*;
-
-/// Defines an enum that wraps the same renderable item
-/// but discriminates on the variant which wraps it.
-///
-/// It also has a special `_Unused` variant which wraps
-/// the engine type using `PhantomData` to permit the
-/// double generic.
-macro_rules! content_enum {
-    ($Enum:ident: $($Variant:ident),+ $(,)?) => {
-        pub enum $Enum<E: Engine, T: Content<E>> {
-            _Unused(PhantomData<E>), $($Variant(T)),+
-        }
-    }
-}
-
-/// Defines an enum that transforms its content
-/// along either the X axis, the Y axis, or both.
-macro_rules! transform_xy {
-    ($self:ident : $Enum:ident |$to:ident|$area:expr) => {
-        content_enum!($Enum: X, Y, XY);
-        impl<E: Engine, T: Content<E>> $Enum<E, T> {
-            pub fn x (item: T) -> Self { Self::X(item) }
-            pub fn y (item: T) -> Self { Self::Y(item) }
-            pub fn xy (item: T) -> Self { Self::XY(item) }
-        }
-        impl<E: Engine, T: Content<E>> Content<E> for $Enum<E, T> {
-            fn content (&self) -> impl Content<E> {
-                match self {
-                    Self::X(item)    => item,
-                    Self::Y(item)    => item,
-                    Self::XY(item)   => item,
-                    _ => unreachable!()
-                }
-            }
-            fn area (&$self, $to: <E as Engine>::Area) -> <E as Engine>::Area {
-                $area
-            }
-        }
-    }
-}
-
-transform_xy!(self: Fill |to|{
-    let [x0, y0, wmax, hmax] = to.xywh();
-    let [x, y, w, h] = Content::area(&self.content(), to).xywh();
-    return match self {
-        Self::X(_)  => [x0, y, wmax, h],
-        Self::Y(_)  => [x, y0, w, hmax],
-        Self::XY(_) => [x0, y0, wmax, hmax],
-        _ => unreachable!()
-    }.into()
-});
-
-/// Defines an enum that transforms its content parametrically
-/// along either the X axis, the Y axis, or both
-macro_rules! transform_xy_unit {
-    (|$self:ident : $Enum:ident, $to:ident|$area:expr) => {
-        pub enum $Enum<E: Engine, T: Content<E>> {
-            X(E::Unit, T), Y(E::Unit, T), XY(E::Unit, E::Unit, T),
-        }
-        impl<E: Engine, T: Content<E>> $Enum<E, T> {
-            pub fn x (x: E::Unit, item: T) -> Self { Self::X(x, item) }
-            pub fn y (y: E::Unit, item: T) -> Self { Self::Y(y, item) }
-            pub fn xy (x: E::Unit, y: E::Unit, item: T) -> Self { Self::XY(x, y, item) }
-            pub fn dx (&self) -> E::Unit {
-                match self {
-                    Self::X(x, _)     => *x,
-                    Self::Y(_, _)     => E::Unit::zero(),
-                    Self::XY(x, _, _) => *x,
-                }
-            }
-            pub fn dy (&self) -> E::Unit {
-                match self {
-                    Self::X(_, _)     => E::Unit::zero(),
-                    Self::Y(y, _)     => *y,
-                    Self::XY(_, y, _) => *y,
-                }
-            }
-        }
-        impl<E: Engine, T: Content<E>> Content<E> for $Enum<E, T> {
-            fn content (&self) -> impl Content<E> {
-                Some(match self {
-                    Self::X(_, content)     => content,
-                    Self::Y(_, content)     => content,
-                    Self::XY(_, _, content) => content,
-                })
-            }
-            fn area (&$self, $to: E::Area) -> E::Area {
-                $area.into()
-            }
-        }
-    }
-}
-
-transform_xy_unit!(|self: Fixed, area|{
-    let area = self.content().area(area);
-    match self {
-        Self::X(fw, _) => [area.x(), area.y(), *fw, area.h()],
-        Self::Y(fh, _) => [area.x(), area.y(), area.w(), *fh],
-        Self::XY(fw, fh, _) => [area.x(), area.y(), *fw, *fh], // tagn
-    }
-});
-
-transform_xy_unit!(|self: Shrink, area|{
-    let area = self.content().area(area);
-    [area.x(), area.y(), area.w().minus(self.dx()), area.h().minus(self.dy())]
-});
-
-transform_xy_unit!(|self: Expand, area|{
-    let area = self.content().area(area);
-    [area.x(), area.y(), area.w() + self.dx(), area.h() + self.dy()]
-});
-
-transform_xy_unit!(|self: Min, area|{
-    let area = self.content().area(area);
-    match self {
-        Self::X(mw, _)      => [area.x(), area.y(), area.w().max(*mw), area.h()],
-        Self::Y(mh, _)      => [area.x(), area.y(), area.w(),          area.h().max(*mh)],
-        Self::XY(mw, mh, _) => [area.x(), area.y(), area.w().max(*mw), area.h().max(*mh)]
-    }});
-
-transform_xy_unit!(|self: Max, area|{
-    let area = self.content().area(area);
-    match self {
-        Self::X(mw, _)      => [area.x(), area.y(), area.w().min(*mw), area.h()],
-        Self::Y(mh, _)      => [area.x(), area.y(), area.w(),          area.h().min(*mh)],
-        Self::XY(mw, mh, _) => [area.x(), area.y(), area.w().min(*mw), area.h().min(*mh)],
-    }});
-
-transform_xy_unit!(|self: Push, area|{
-    let area = self.content().area(area);
-    [area.x() + self.dx(), area.y() + self.dy(), area.w(), area.h()]
-});
-
-transform_xy_unit!(|self: Pull, area|{
-    let area = self.content().area(area);
-    [area.x().minus(self.dx()), area.y().minus(self.dy()), area.w(), area.h()]
-});
-
-transform_xy_unit!(|self: Margin, area|{
-    let area = self.content().area(area);
-    let dx = self.dx();
-    let dy = self.dy();
-    [area.x().minus(dx), area.y().minus(dy), area.w() + dy + dy, area.h() + dy + dy]
-});
-
-transform_xy_unit!(|self: Padding, area|{
-    let area = self.content().area(area);
-    let dx = self.dx();
-    let dy = self.dy();
-    [area.x() + dx, area.y() + dy, area.w().minus(dy + dy), area.h().minus(dy + dy), ]
-});
-
-#[derive(Default, Debug, Copy, Clone)]
-pub enum Alignment { #[default] Center, X, Y, NW, N, NE, E, SE, S, SW, W }
-
-pub struct Align<E: Engine, T: Content<E>>(Alignment, T, PhantomData<E>);
-
-impl<E: Engine, T: Content<E>> Align<E, T> {
-    pub fn c  (w: T) -> Self { Self(Alignment::Center, w, Default::default()) }
-    pub fn x  (w: T) -> Self { Self(Alignment::X, w, Default::default())      }
-    pub fn y  (w: T) -> Self { Self(Alignment::Y, w, Default::default())      }
-    pub fn n  (w: T) -> Self { Self(Alignment::N, w, Default::default())      }
-    pub fn s  (w: T) -> Self { Self(Alignment::S, w, Default::default())      }
-    pub fn e  (w: T) -> Self { Self(Alignment::E, w, Default::default())      }
-    pub fn w  (w: T) -> Self { Self(Alignment::W, w, Default::default())      }
-    pub fn nw (w: T) -> Self { Self(Alignment::NW, w, Default::default())     }
-    pub fn sw (w: T) -> Self { Self(Alignment::SW, w, Default::default())     }
-    pub fn ne (w: T) -> Self { Self(Alignment::NE, w, Default::default())     }
-    pub fn se (w: T) -> Self { Self(Alignment::SE, w, Default::default())     }
-}
-
-impl<E: Engine, T: Content<E>> Content<E> for Align<E, T> {
-    fn area (&self, outer: E::Area) -> E::Area {
-        align_areas(self.0, outer.xywh(), Content::area(&self.content(), outer).xywh()).into()
-    }
-    fn render (&self, render: &mut E::Output) {
-        render.place(self.area(render.area()), &self.content())
-    }
-}
-
-pub fn align_areas<N: Coordinate>(alignment: Alignment, on: [N;4], it: [N;4]) -> [N;4] {
-    let [cfx, cfy] = on.center();
-    let [cmx, cmy] = it.center();
-    let center     = |cf, cm, m: N|if cf >= cm { m + (cf - cm) } else { m.minus(cm - cf) };
-    let center_x   = center(cfx, cmx, it.x());
-    let center_y   = center(cfy, cmy, it.y());
-    let east_x     = on.x() + on.w().minus(it.w());
-    let south_y    = on.y() + on.h().minus(it.h());
-    match alignment {
-        Alignment::Center => [center_x, center_y, it.w(), it.h()],
-        Alignment::X      => [center_x, it.y(),   it.w(), it.h()],
-        Alignment::Y      => [it.x(),   center_y, it.w(), it.h()],
-
-        Alignment::NW     => [on.x(),   on.y(),   it.w(), it.h()],
-        Alignment::N      => [center_x, on.y(),   it.w(), it.h()],
-        Alignment::NE     => [east_x,   on.y(),   it.w(), it.h()],
-        Alignment::E      => [east_x,   center_y, it.w(), it.h()],
-        Alignment::SE     => [east_x,   south_y,  it.w(), it.h()],
-        Alignment::S      => [center_x, south_y,  it.w(), it.h()],
-        Alignment::SW     => [on.x(),   south_y,  it.w(), it.h()],
-        Alignment::W      => [on.x(),   center_y, it.w(), it.h()],
-    }
-}
-
-//fn align<E: Engine, T: Content<E>, N: Coordinate, R: Area<N> + From<[N;4]>> (align: &Align<E, T>, outer: R, content: R) -> Option<R> {
-    //if outer.w() < content.w() || outer.h() < content.h() {
-        //None
-    //} else {
-        //let [ox, oy, ow, oh] = outer.xywh();
-        //let [ix, iy, iw, ih] = content.xywh();
-        //Some(match align {
-            //Align::Center(_) => [ox + (ow - iw) / 2.into(), oy + (oh - ih) / 2.into(), iw, ih,].into(),
-            //Align::X(_)  => [ox + (ow - iw) / 2.into(), iy, iw, ih,].into(),
-            //Align::Y(_)  => [ix, oy + (oh - ih) / 2.into(), iw, ih,].into(),
-            //Align::NW(_) => [ox, oy, iw, ih,].into(),
-            //Align::N(_)  => [ox + (ow - iw) / 2.into(), oy, iw, ih,].into(),
-            //Align::NE(_) => [ox + ow - iw, oy, iw, ih,].into(),
-            //Align::W(_)  => [ox, oy + (oh - ih) / 2.into(), iw, ih,].into(),
-            //Align::E(_)  => [ox + ow - iw, oy + (oh - ih) / 2.into(), iw, ih,].into(),
-            //Align::SW(_) => [ox, oy + oh - ih, iw, ih,].into(),
-            //Align::S(_)  => [ox + (ow - iw) / 2.into(), oy + oh - ih, iw, ih,].into(),
-            //Align::SE(_) => [ox + ow - iw, oy + oh - ih, iw, ih,].into(),
-            //_ => unreachable!()
-        //})
-    //}
-//}
diff --git a/layout/src/transform_xy.rs b/layout/src/transform_xy.rs
new file mode 100644
index 00000000..7ede48d8
--- /dev/null
+++ b/layout/src/transform_xy.rs
@@ -0,0 +1,41 @@
+use crate::*;
+
+/// Defines an enum that transforms its content
+/// along either the X axis, the Y axis, or both.
+///
+/// The `_Unused` variant wraps the `Engine` type
+/// using `PhantomData` to permit the double generic.
+macro_rules! transform_xy {
+    ($self:ident : $Enum:ident |$to:ident|$area:expr) => {
+        pub enum $Enum<E: Engine, T: Content<E>> { _Unused(PhantomData<E>), X(T), Y(T), XY(T) }
+        impl<E: Engine, T: Content<E>> $Enum<E, T> {
+            pub fn x (item: T) -> Self { Self::X(item) }
+            pub fn y (item: T) -> Self { Self::Y(item) }
+            pub fn xy (item: T) -> Self { Self::XY(item) }
+        }
+        impl<E: Engine, T: Content<E>> Content<E> for $Enum<E, T> {
+            fn content (&self) -> impl Content<E> {
+                match self {
+                    Self::X(item)    => item,
+                    Self::Y(item)    => item,
+                    Self::XY(item)   => item,
+                    _ => unreachable!()
+                }
+            }
+            fn area (&$self, $to: <E as Engine>::Area) -> <E as Engine>::Area {
+                $area
+            }
+        }
+    }
+}
+
+transform_xy!(self: Fill |to|{
+    let [x0, y0, wmax, hmax] = to.xywh();
+    let [x, y, w, h] = Content::area(&self.content(), to).xywh();
+    return match self {
+        Self::X(_)  => [x0, y, wmax, h],
+        Self::Y(_)  => [x, y0, w, hmax],
+        Self::XY(_) => [x0, y0, wmax, hmax],
+        _ => unreachable!()
+    }.into()
+});
diff --git a/layout/src/transform_xy_unit.rs b/layout/src/transform_xy_unit.rs
new file mode 100644
index 00000000..6f7984a1
--- /dev/null
+++ b/layout/src/transform_xy_unit.rs
@@ -0,0 +1,101 @@
+use crate::*;
+
+/// Defines an enum that parametrically transforms its content
+/// along either the X axis, the Y axis, or both.
+macro_rules! transform_xy_unit {
+    (|$self:ident : $Enum:ident, $to:ident|$area:expr) => {
+        pub enum $Enum<E: Engine, T: Content<E>> {
+            X(E::Unit, T), Y(E::Unit, T), XY(E::Unit, E::Unit, T),
+        }
+        impl<E: Engine, T: Content<E>> $Enum<E, T> {
+            pub fn x (x: E::Unit, item: T) -> Self { Self::X(x, item) }
+            pub fn y (y: E::Unit, item: T) -> Self { Self::Y(y, item) }
+            pub fn xy (x: E::Unit, y: E::Unit, item: T) -> Self { Self::XY(x, y, item) }
+            pub fn dx (&self) -> E::Unit {
+                match self {
+                    Self::X(x, _)     => *x,
+                    Self::Y(_, _)     => E::Unit::zero(),
+                    Self::XY(x, _, _) => *x,
+                }
+            }
+            pub fn dy (&self) -> E::Unit {
+                match self {
+                    Self::X(_, _)     => E::Unit::zero(),
+                    Self::Y(y, _)     => *y,
+                    Self::XY(_, y, _) => *y,
+                }
+            }
+        }
+        impl<E: Engine, T: Content<E>> Content<E> for $Enum<E, T> {
+            fn content (&self) -> impl Content<E> {
+                Some(match self {
+                    Self::X(_, content)     => content,
+                    Self::Y(_, content)     => content,
+                    Self::XY(_, _, content) => content,
+                })
+            }
+            fn area (&$self, $to: E::Area) -> E::Area {
+                $area.into()
+            }
+        }
+    }
+}
+
+transform_xy_unit!(|self: Fixed, area|{
+    let area = self.content().area(area);
+    match self {
+        Self::X(fw, _) => [area.x(), area.y(), *fw, area.h()],
+        Self::Y(fh, _) => [area.x(), area.y(), area.w(), *fh],
+        Self::XY(fw, fh, _) => [area.x(), area.y(), *fw, *fh], // tagn
+    }
+});
+
+transform_xy_unit!(|self: Shrink, area|{
+    let area = self.content().area(area);
+    [area.x(), area.y(), area.w().minus(self.dx()), area.h().minus(self.dy())]
+});
+
+transform_xy_unit!(|self: Expand, area|{
+    let area = self.content().area(area);
+    [area.x(), area.y(), area.w() + self.dx(), area.h() + self.dy()]
+});
+
+transform_xy_unit!(|self: Min, area|{
+    let area = self.content().area(area);
+    match self {
+        Self::X(mw, _)      => [area.x(), area.y(), area.w().max(*mw), area.h()],
+        Self::Y(mh, _)      => [area.x(), area.y(), area.w(),          area.h().max(*mh)],
+        Self::XY(mw, mh, _) => [area.x(), area.y(), area.w().max(*mw), area.h().max(*mh)]
+    }});
+
+transform_xy_unit!(|self: Max, area|{
+    let area = self.content().area(area);
+    match self {
+        Self::X(mw, _)      => [area.x(), area.y(), area.w().min(*mw), area.h()],
+        Self::Y(mh, _)      => [area.x(), area.y(), area.w(),          area.h().min(*mh)],
+        Self::XY(mw, mh, _) => [area.x(), area.y(), area.w().min(*mw), area.h().min(*mh)],
+    }});
+
+transform_xy_unit!(|self: Push, area|{
+    let area = self.content().area(area);
+    [area.x() + self.dx(), area.y() + self.dy(), area.w(), area.h()]
+});
+
+transform_xy_unit!(|self: Pull, area|{
+    let area = self.content().area(area);
+    [area.x().minus(self.dx()), area.y().minus(self.dy()), area.w(), area.h()]
+});
+
+transform_xy_unit!(|self: Margin, area|{
+    let area = self.content().area(area);
+    let dx = self.dx();
+    let dy = self.dy();
+    [area.x().minus(dx), area.y().minus(dy), area.w() + dy + dy, area.h() + dy + dy]
+});
+
+transform_xy_unit!(|self: Padding, area|{
+    let area = self.content().area(area);
+    let dx = self.dx();
+    let dy = self.dy();
+    [area.x() + dx, area.y() + dy, area.w().minus(dy + dy), area.h().minus(dy + dy), ]
+});