Search and Styling
InDesign GREP Find/Change can match patterns in text and perform defined replacements. A GREP style applies a character style to matching text through a paragraph style; it does not rewrite the text.
A Small Starting Example
The expression \d+ matches a run of digits. That can be useful for finding numbers, but it does not know whether the number is a date, a page reference or part of an identifier. Context and scope still matter.
Use a Controlled Sequence
Save a copy, try the expression on representative text, inspect every class of match and only then apply it more widely. Record search scope and options. A reusable pattern should state its assumptions and known exceptions.
Further Reading: helpx.adobe.com