| UsingOpen = "using" NamespaceOrType ";";
| UsingAlias = "using" Name "=" NamespaceOrType ";";
Using directives are very similar to the ones used in C#. Their purpose is to shorten names.
UsingOpen lets you open up a
SyntaxModule and a type, after which the opened character can be addressed with a short name. For example:
UsingAlias you to create an alias for a type or
SyntaxModule. For example:
using Token = Nitra.NSpan;