The get argument function

gistfile1.php

<?php
  /**
   * This function controls what to return to the contextual filter.
   */
  function get_argument() {
    // Get available flag types from the system.
    $flags = flag_get_flags('taxonomy_term');

    // Get all User flags.
    $user_flags = flag_get_user_flags('taxonomy_term');
   
    // This array will collect all Term IDs which will be filtered.
    $tids = array();
   
    // Get the vocab foreach flag.
    foreach ($flags as $flagname => $flag) {
      // We only proceed with this flag, if it has been selected and the current
      // user has flagged terms with that flag.
      if (!empty($this->options['flags'][$flagname]) && !empty($user_flags[$flagname])) {
        // Get all tids from the user flags.
        $user_tids = array_keys($user_flags[$flagname]);
        $vocabs = array();
        // Check  which vocabularies are valid for this handler.
        foreach ($flag->types as $vocab) {
          if (!empty($this->options['vocabularies'][$vocab])) {
            $vocabs[] = $vocab;
          }
        }
        // We add the valid terms of the flag set to our default argument list.
        $valid_tids = _views_flag_context_filter_tids_on_vocabularies($user_tids, $vocabs);
        $tids = array_merge($tids, $valid_tids);
      }
    }
    // If no tids are valid, we can fallback to a given value.
    if (empty($tids)) {
      // Fall back to the exception value (by default this is 'all')
      return $this->options['fallback'];
    }
    // If there are term ids available we return them by concating the terms
    // with the multiple operator (AND or OR).
    else {
      return implode($this->options['multiple_operator'], $tids);
    }
  }