The ''regexp'' filter operator filters tiddlers that match a regular expression.
Regular expressions are a way of encoding complex string matching criteria. The format is defined fully in [[this Mozilla reference|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions]].
The regexp filter operator takes a fieldname as the optional suffix (defaulting to `title`).
The regular expression itself can start or end with an optional string to specify flags in the format `(?flags)` where flags can be "g", "m" or "i". Only the "i" flag is generally useful: it forces the match to be case-insensitive (ie upper and lower case letters are considered the same).
For example:
|!Filter String |!Description |
|`[all[tiddlers]regexp[EggCup]]` |Selects all tiddlers that have the CamelCase string "EggCup" in their title |
|`[all[tiddlers]regexp[eggcup(?i)]]` |Selects all tiddlers that have the string "eggcup" in their title (ignoring case) |
