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 — Gets a specific external variable by name and optionally filters it
• filter_input_array — Gets external variables and optionally filters them
• filter_list — Returns a list of all supported filters
• filter_var — Filters a variable with a specified filter
• filter_var_array — Gets multiple variables and optionally filters them