docs: def _with(self, option=None):
          """Check if a build option is enabled.
  
          If called without argument, it returns all WITH_* items.
  
          Example:
  
              {% if with('foo') %}...{% endif %}
          """
          if option is None:
              return (
                  (k, v) for k, v in self.env.items()
                  if k.startswith('WITH_')
              )
          return self.env.get('WITH_' + option.upper()) == True