Whether a handle has a screen below it by its type: required for a handle an edge reached (the edge pushed it over its opener), optional for one that may be a root (a retrace, a restore, an opener back returns).
required
optional
back
Whether a handle has a screen below it by its type:
requiredfor a handle an edge reached (the edge pushed it over its opener),optionalfor one that may be a root (a retrace, a restore, an openerbackreturns).