xcall MIAMEX, MX_RELEASEKBD {,opcode}
If opcode is zero or omitted, the keyboard hold is released. If opcode is anything else, the keyboard hold is set.
History
A-Shell build 946.1 of 17 Nov 2005 introduced a new and improved internal protocol for communications between the application and GUI front-end. One aspect of this new protocol involved setting and releasing keyboard holds so that keyboard input and GUI command responses did not get mixed together. MIAMEX 153 is used to control that keyboard hold. The application programmer will, under normal circumstances, never need this command, since A-Shell should take care of it automatically. It is nonetheless documented and made available for programmer use in case of some as-yet-unforeseen situation.