function _getBinding(bindingName) {
    for (var i = _scopeStack.length - 1 ; i >= 0; --i) {
      var scopeBindings = _scopeStack[i]["(bindings)"];
      if (scopeBindings[bindingName]) {
        return scopeBindings;
      }
    }
  }
Find the relevant binding's scope. The owning scope is located by first
inspecting the current scope and then moving "downward" through the stack
of scopes.

@param {string} bindingName - the value of the identifier

@returns {Object} - the scope in which the binding was found