In vfp ,the helpstring is used as well in class description.if you modify any class :
modi class ?
see the attached photo.
in the menu clicking on item " class information" fires a dialog with a description field...
this field can store 255 chars maxi.
even if it filled with more chars it retains only 255 chars ( as max capacity string in vfp).
if you open the class as table, can see this description stored in a memo fileld "reserved7"...
theorically can store a great quantity of chars but it troncated to 255 chars.

for more issue in command window(on by one+return):

help DEFINE CLASS Command
help Visual FoxPro and Advanced COM
help DEFINE CLASS Command - PEMName_COMATTRIB Clause
help VFPXMLProgID Property