[Issue 15475] Ddoc code sample with unbalanced paren comes out as macro

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=15475

--- Comment #4 from hsteoh at quickfur.ath.cx ---
Found that the problem is that the ')' is doubly-escaped: by the time it gets
to highlightText(), it's already escaped, but highlightText doesn't know that,
and when it calls highlightCode2() it escapes it a second time, turning
`$(RPAREN)` (which would have correctly expanded into ')') into
`$(DOLLAR)$(LPAREN)RPAREN$(RPAREN)`, so it expands back to `$(PAREN)` instead.

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