begin-metadata-changes in drscheme:unit:definitions-text<%>
Augment this method to be notified when DrScheme is changing
the buffer to insert metadata. The metadata is only inserted
during saving, so tools that track changes to DrScheme will
need to ignore changes that occur after this method is
called, and before
end-metadata-changes is called.
A call to begin-metadata-changes will always be
followed with a call to end-metadata-changes (ie,
the calls cannot be nested).