You can use meta-characters in the 'Search For' field:
| . | any character except newline | + | one or more times |
| * | zero or more times | ? | zero or one time |
| {n} | match exact n times | {n,m} | at least n, at most m times |
| | | pipe: a|b matches a or b | - | hyphen, match a range of chars |
| ^ | beginning of a line | $ | end of a line |
| [...] | one of the char's of a set | [^...] | negated character set |
| \b | word boundary | \B | word non boundary |
| \d | numeral [0-9] | \D | non numeral [^0-9] |
| \s | single white space | \S | single non white space |
| \w | [A-Za-z0-9_] | \W | [^A-Za-z0-9_] |
| (...) | grouping are stored as $1..$9 | \. | escape a meta char |
The 'Replace with' field can use $1..$9 as a backreference to parentheses of 'Search for' field.
Example:
Search for /abc|def/ will match the word 'abc' or the word 'def'
Search for /bwiki/b will match the word 'wiki' but not the word 'jspwiki'.
Search for ^[IVXMDCL]+\. will match any combination of roman numeral char's followed by a period
Search for /(-?\d+)(\d{3})/ and replace with $1,$2 to insert commas in large integers.
This is the EditFindAndReplaceHelp page.
More info on regular expressions
and RegExp Sandbox