Per-line `$…$` scanning with the Pandoc guards F5 required: an opener must be
followed by a non-space, a closer must be preceded by a non-space and not
followed by a digit, and `\$` escapes. Without them "prices are $5 and $6
today" renders "5 and " as math, in exactly the grammar-less prose buffers
this scanner targets. Spans never cross a newline (Q#MS3), so callers scan one
line at a time.
`$$` is opaque, and the test that forced this is worth keeping in mind. My
first version simply refused to OPEN on `$$`, reasoning that display math
would then never match. It still did: in `$$x$$` the first `$` declines to
open, the second one opens, and the third closes it — matching the inner `$x$`,
whose interior parses perfectly well. So display math would have half-rendered
as math with a stray `$` on each side, which is precisely what acceptance 15
forbids. `$$` now neither opens nor closes and abandons any pending opener.
The test that caught it was itself nearly vacuous. It asserted "every span
found must fail to parse", which passes trivially when the matched interior is
`x`. Asserting that NO span is found is the form that actually holds the
contract; the weaker version would have shipped the bug.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Levi Neuwirth
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