Word filter
This filter use regexp. Examples:
abc = all words containing 'abc'
^abc = all words starting with 'abc'
abc$ = all words ending with 'abc'
The character . can replace any character:
^abc.. = all words of at least 5 letters starting with 'abc'
^...$ = all 4-letter word
^ab.c$ = all 4-letter word beginning with 'ab' and ending with 'c'
For more information on regular expressions: http://en.wikipedia.org/wiki/Regular_expression