Ordinary Characters
Ordinary characters consist of all printable and non-printable characters that are not explicitly designated as metacharacters. This includes all uppercase and lowercase alphabetic characters, all digits, all punctuation marks, and some symbols.
Simple Expressions
The simplest form of a regular expression is a single, ordinary character that matches itself in a searched string. For example, a single-character pattern, such as A, matches the letter A wherever it appears in the searched string. Here are some examples of single-character regular expression patterns:
/a/
/7/
/M/
You can combine a number of single characters to form a large expression. For example, the following regular expression combines the single-character expressions: a, 7, and M.
/a7M/
Notice that there is no concatenation operator. You just type one character after another.