docs: function processDecl(result, decl, opts) {
      const promises = [];
  
      decl.value = valueParser(decl.value).walk(node => {
          if (
              node.type !== 'function' ||
              node.value !== 'url' ||
              node.nodes.length === 0
          ) {
              return;
          }
  
          const promise = Promise.resolve()
              .then(() => processUrl(result, decl, node.nodes[0], opts))
              .catch(err => {
                  decl.warn(result, err.message);
              });
  
          promises.push(promise);
      });
  
      return Promise.all(promises).then(() => decl);
  }