Add menu to Context menu

Dear all,

In a script I try to add a menu item to an existing context menu:

menuLocation = app.GetNamedMenu (!TextContextMenu);
oCmd.cmdDoc = menuLocation.DefineAndAddCommand (1, "ETB_InsertSymbol", "Insert special symbol [ETB]", ""); 

It is not a problem to do so in the menu.cfg file - but in the script it fails with error message

TextContextMenu is undefined

Note, that the ! has gone here.

It seems that scripts can't add to context menus.

What's Your opinion here?