ctype_xdigit
Introduction
Variable and Type Related Extensions
PHP Manual

# Data Filtering

- Introduction
- Installing/Configuring
  - Installation
  - Runtime Configuration
  - Resource Types
- Predefined Constants
- Filter Functions
  - filter_has_var — Checks if variable of specified type exists
  - filter_id — Returns the filter ID belonging to a named filter
  - filter_input_array — Gets external variables and optionally filters them
  - filter_input — Gets a specific external variable by name and optionally filters it
  - filter_list — Returns a list of all supported filters
  - filter_var_array — Gets multiple variables and optionally filters them
  - filter_var — Filters a variable with a specified filter

ctype_xdigit
Introduction
Variable and Type Related Extensions
PHP Manual