Include file:
When a tree of graphical components is saved to disk (translated to ASCII), it is
possible to enable the output of point-lists first as 'pts' records, to allow
for compression of replicated point lists within a single document. When reading
these documents back in, the istream constructor of OverlayIdrawComp (and other
top-level components) uses this mixin to manage a table of point lists, building
it up as each 'pts' record is read, and accessing entries for each ":pts id" field
found in subsequent records.