pub const MODE_CODE: char = '\u{E000}';Expand description
Reserved private-use markers that the Quarto filter inserts around a segment so a single invocation can switch mid-stream between rule sets. Source authors never type these, which is why they live in the Unicode Private Use Area.
A marker means “everything after me is this kind of segment, until the next marker”. Structure that markdown expresses and a flat string cannot — a heading is not a paragraph that happens to be short — has to cross the boundary somehow, and this is the seam it crosses.
Wire protocol note: extensions/vertext/vertext.lua carries the same
codepoints as string literals. The mode_markers_are_the_wire_protocol
test pins the values so a drift on the Rust side cannot pass silently.