host is readonly in this contract because only the registry writes
it: implementations declare it as a plain mutable field (see
ComponentHostBinding) initialized to null, and
ComponentRegistry assigns it on attach and clears it on detach.
Application code must never assign host.
Typed behavior/state attached to a host.
hostisreadonlyin this contract because only the registry writes it: implementations declare it as a plain mutable field (see ComponentHostBinding) initialized tonull, and ComponentRegistry assigns it on attach and clears it on detach. Application code must never assignhost.