Regular Expressions

Regular expressions (often called regex or regexp) are patterns used to match, search and manipulate text.
They provide a compact way to describe text structures such as email addresses, dates, numbers, words, or any other textual pattern.

link - regexone.com

VBA Built-in Classes

Starting with Office 365, Version 2508, There are four built-in classes that can handle regular expressions.
RegExp - The main regular expression engine (pattern, options, execution).
Match - Represents a single match result.
MatchCollection - A collection of all matches returned by a RegExp execution.
SubMatches - A collection of captured groups (parentheses) within a match.
These are the same objects as the VBScript libray except they are built-in to VBA so you do not need any external reference.

Microsoft VBScript Regular Expressions 5.5

In earlier versions you had to add a reference to an additional library.

link - devblogs.microsoft.com/microsoft365dev/how-to-prepare-vba-projects-for-vbscript-deprecation/ 
link - learn.microsoft.com/en-us/previous-versions/windows/internet-explorer/ie-developer/scripting-articles/ms974570(v=msdn.10)

Code Snippets

Matching Exact 2 Characters

Matching Any 3 Digits

The "\d" can match any digit, equivalent to [0-9]

Matching Any 3 Characters

The "." will match any letter, digit, whitespace, everything except \n

Matching Any 3 Non Digits

The "\D" will match any non digit, equivalent to [^0-9]

Matching A Full Stop

The "\." will match a full stop

Matching Certain Characters

The "[et]" will match single "e" and "t" characters

Matching Excluding Characters

The "[^et]" will match everything that doesn't contain the single characters "e" and "t"

Matching Any Alphanumeric Characters

The "\w" will match all letters and numbers, equivalent to [A-Za-z0-9]

Matching Any 3 Letters with the first one in uppercase

Matching Repetition

This will match "aaaa"

This will match ??

This will match any characters repeated 2,3 or 4 times

Matching Zero or More Repetitions

The "*" will match zero or more repetitions

This will match any number of a's, b's and c's

Matching One or More Repetitions

The "+" will match one or more repetitions

Matching Optional Characters

The "?" will match optional characters
This will make the "b" an optional character

Matching Whitespace

The "\s" will match any single space, tab character, new line or carriage return character