Some applications may use the expression editor in a special mode in which placeholders may be defined. A placeholder is a part of some expression that can be given a name by the user at runtime. Placeholders are used to support user-defined “template” expressions in which named portions of the template can be later changed.
In a grammar definition file, you can enclose any construct in a <placeholder>...</placeholder> wrapper to indicate that it should be treated as a placeholder.
