The simplest and most common type of regex is an alphanumeric string that matches itself, called a "literal text match". A literal text regex matches anywhere along a string. For example, a literal string matches itself when placed alone, and at the beginning, middle, or end of a larger string. Literal text matches are case sensitive.
Example 1: Search for the string "at".
at
at math hat ate
it a-t At
Example 2: Search for the string "email".
email emailing many_emails
Email EMAILing e-mails
Example 3: Search for the string "abcdE567".
abcdE567
abcdE567 AabcdE567ing text_abcdE567
SPAMabCdE567 ABCDe567