A regular expression is a way of specifying an ambiguous pattern to search for. Regular expressions are commonly used in some computer programming languages and may be more familiar to some users than to others. This is the OR operator to enable a match to be made to either one pattern OR another. There is no AND operator in this version of regular expressions. You may have one or more characters in this set.
Regular expressions are case-sensitive.
The pattern 'AAAA' will not match the sequence 'aaaa'. Here is a sample session with preg. Warnings Regular expressions are case-sensitive. The pattern 'AAAA' will not match the sequence 'aaaa'. Diagnostic Error Messages None.