Pops the current meta off the stack, optionally checking that the classname is correct
function(className) {
      if (!this.__metaStack.length) {
        throw new Error("No __metaStack entries to pop"); 
      }
      let meta = this.__metaStack[this.__metaStack.length - 1];
      if (className && meta.className != className) {
        throw new Error("Wrong __metaStack entries to pop, expected " + className + " found " + meta.className); 
      }
      this.__metaStack.pop();
      meta = this.__metaStack[this.__metaStack.length - 1] || null;
      this.__classMeta = meta;
    }