question: private StrBuilder replaceImpl ( final StrMatcher matcher , final String replaceStr , final int from , int to , int replaceCount ) { if ( matcher == null || size == 0 ) { return this ; } final int replaceLen = ( replaceStr == null ? 0 : replaceStr . length ( ) ) ; final char [ ] buf = buffer ; for ( int i = from ; i < to && replaceCount != 0 ; i ++ ) { final int removeLen = matcher . isMatch ( buf , i , from , to ) ; if ( removeLen > 0 ) { replaceImpl ( i , i + removeLen , removeLen , replaceStr , replaceLen ) ; to = to - removeLen + replaceLen ; i = i + replaceLen - 1 ; if ( replaceCount > 0 ) { replaceCount -- ; } } } return this ; }
target:  Replaces within the builder using a matcher. <p> Matchers can be used to perform advanced behaviour. For example you could write a matcher to delete all occurrences where the character 'a' is followed by a number.