docs: function checkActionBlock(src, yylloc) {
      // make sure reasonable line numbers, etc. are reported in any
      // potential parse errors by pushing the source code down:
      if (yylloc && yylloc.first_line > 0) {
          var cnt = yylloc.first_line + 1;
          var lines = new Array(cnt);
          src = lines.join('\n') + src;
      } 
      if (!src.trim()) {
          return false;
      }
  
      try {
          parseCodeChunkToAST(src);
          return false;
      } catch (ex) {
          return ex.message || "code snippet cannot be parsed";
      }
  }