PHP provides a set of functions that let you work with regular expressions, which are patterns used to search, match, or manipulate text.

Regular expressions are written between / / and are commonly used to validate input, search for specific values, or filter data.

The most common PHP regex functions are:

• preg_match()
  Checks if a pattern exists in a string.
  Returns 1 if a match is found, 0 if not.
  Best used for yes/no checks inside if statements.
• preg_match_all()
  Counts how many times a pattern appears in a string.
  Useful when you need the total number of matches instead of just knowing whether one exists.
• preg_replace()
  Replaces all matches of a pattern with another value and returns the modified string.
  Commonly used for cleaning or transforming text.
• preg_split()
  Splits a string into an array using a regular expression as the separator.
  Helpful when simple delimiters like commas or spaces are not enough.
• preg_grep()
  Filters an array and returns only the values that match a pattern.
  With PREG_GREP_INVERT, it returns values that do not match.

Important regex concepts introduced:

• Patterns go between / /
• Some characters like . must be escaped using \
• Parentheses ( ) are used for grouping parts of a pattern
• Regex can be case-insensitive using the i modifier

At this stage, the main goal is not to master regex syntax, but to understand which function to use and how regex integrates naturally with conditionals and arrays in PHP.