For the sake of readability, consistency and to make further changes
easier, introduce named groups (?<text>) and (?<url>) to all link
parsing regexes which have parts containing the desired link text
and (optionally) URL.
The introduction of the named groups additionally simplifies
handleMatches() and makes all calls to it consistent.
For users to be able to add square brackets inside of links using
the new format, the regular expression used for parsing those links
contained a balancing group, which can be used for matching pairs
of tokens (in this case, opening and closing brackets, in that order).
However, this means that users could not post links with unmatched
brackets inside of them (ie. ones that contain single brackets, or
a closing bracket and then an opening one). Allow for escaping opening
and closing brackets using the backslash character.
The change substitutes this old fragment of the regex in the display
text group:
[^\[\]]* // any character other than closing/opening bracket
for this one:
(((?<=\\)[\[\]])|[^\[\]])*
The second pattern in the alternative remains the same; the first one
performs the escaping, as follows:
(
(?<=\\) // positive lookbehind expression:
// this match will succeed, if the next expression
// is preceded by a single backslash
[\[\]] // either an opening or closing brace
)
Since the entire display group is matched, unfortunately the lookbehind
expression does not actually strip the backslashes, so they are
manually stripped in handleMatches.
As demonstrated in the unit tests attached, this also allows balanced
brackets to be mixed with escaped ones.
