Interpret vertical page number alignment differently

The vertical alignment of `number-align` now selects header or footer instead of aligning within the footer. This is a minor breaking change because
- top behaves differently now
- horizon is now forbidden
- bottom (the new default) behaves differently, too
Typical number-align usage will likely not use the vertical component at all, though.

Fixes #645

2 files changed, 25 insertions, 0 deletions

diff --git a/tests/ref/layout/page-number-align.png b/tests/ref/layout/page-number-align.png
new file mode 100644
index 00000000..b05ca454
--- /dev/null
+++ b/tests/ref/layout/page-number-align.png
diff --git a/tests/typ/layout/page-number-align.typ b/tests/typ/layout/page-number-align.typ
new file mode 100644
index 00000000..0e9b2bc9
--- /dev/null
+++ b/tests/typ/layout/page-number-align.typ
@@ -0,0 +1,25 @@
+// Test page number alignment.
+
+---
+#set page(
+  height: 100pt,
+  margin: 30pt,
+  numbering: "(1)",
+  number-align: top + right,
+)
+
+#block(width: 100%, height: 100%, fill: aqua.lighten(50%))
+
+---
+#set page(
+  height: 100pt,
+  margin: 30pt,
+  numbering: "[1]",
+  number-align: bottom + left,
+)
+
+#block(width: 100%, height: 100%, fill: aqua.lighten(50%))
+
+---
+// Error: 25-39 page number cannot be `horizon`-aligned
+#set page(number-align: left + horizon)