A regular expression describes a string of characters corresponding to a data type.
For example, the expression a.b, describes all strings of three characters where the first character is "a" and the last character is "b". The middle character can be anything. The expression therefore describes strings such as:
The two characters "a" and "b" simply describe themselves; the period in between them is a place-holder (wildcard) for any alphanumeric or numeric character.
This table summarizes the most important syntactic elements found in regular expressions: