code: private function collectConflictsWithin(
          ValidationContext $context,
          array &$conflicts,
          array $fieldMap
      ) {
          // A field map is a keyed collection, where each key represents a response
          // name and the value at that key is a list of all fields which provide that
          // response name. For every response name, if there are multiple fields, they
          // must be compared to find a potential conflict.
          foreach ($fieldMap as $responseName => $fields) {
              // This compares every field in the list to every other field in this list
              // (except to itself). If the list only has one item, nothing needs to
              // be compared.
              $fieldsLength = count($fields);
              if ($fieldsLength <= 1) {
                  continue;
              }
  
              for ($i = 0; $i < $fieldsLength; $i++) {
                  for ($j = $i + 1; $j < $fieldsLength; $j++) {
                      $conflict = $this->findConflict(
                          $context,
                          false, // within one collection is never mutually exclusive
                          $responseName,
                          $fields[$i],
                          $fields[$j]
                      );
                      if (! $conflict) {
                          continue;
                      }
  
                      $conflicts[] = $conflict;
                  }
              }
          }
      }
docs: Collect all Conflicts "within" one collection of fields.
  
  @param mixed[][] $conflicts
  @param mixed[][] $fieldMap