The APL2® character set is activated by simultaneously pressing the X Window System XK_Backspace key (usually the Backspace key) and the State Mod1Mask key (usually the Alt key). For example, if you use the IBM® 101 Enhanced Keyboard, the APL2 character set is toggled on and off by pressing and holding the Alt key, and then pressing the Backspace key.

When the APL2 character set is active, the characters APL are displayed in the title bar of the GDDMXD/MVS window.

In the X Window System, a key code is assigned to each key on the keyboard. GDDMXD/MVS uses key codes in combination with modifier keys. For example, the Shift and Alt keys determine the data that should be passed back from GDDMXD/MVS to the X Window System application to identify the user’s keystroke data.

GDDMXD looks for the data set SEZAINST(GDXALTCS) when it is initialized. Before using GDDMXD, copy the installed TCP/IP copy of SEZAINST(GDXALTCS) to user_id.GDXALTCS.PSS, or allocate the common installed copy of GDXALTCS.PSS to ddname GDXDACSP.

A default map for the APL2 character set is provided in GDDMXD/MVS, which corresponds to the IBM 101 Key Enhanced Keyboard. You can override this default map by creating a data set called GDXAPLCS.MAP to define the map for your workstation. When GDDMXD/MVS is initialized, the system searches for a data set called GDXAPLCS.MAP. If the GDXAPLCS.MAP data set exists, the data in the GDXAPLCS.MAP data set replaces the default mapping for all keys.