code: public function parseHgIgnoreLine($line)
      {
          if (preg_match('#^syntax\s*:\s*(glob|regexp)$#', $line, $matches)) {
              if ($matches[1] === 'glob') {
                  $this->patternMode = self::HG_IGNORE_GLOB;
              } else {
                  $this->patternMode = self::HG_IGNORE_REGEX;
              }
  
              return null;
          }
  
          if ($this->patternMode == self::HG_IGNORE_GLOB) {
              return $this->patternFromGlob($line);
          }
  
          return $this->patternFromRegex($line);
      }
docs: Callback line parser which process hgignore lines
  
  @param string $line A line from .hgignore
  
  @return array|null An exclude pattern for filter()