efaq: ExtendChar key does not work as Meta
9.14 Why doesn’t my <ExtendChar> key work as a <Meta> key under HP-UX 8.0 and 9.x?
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This is a result of an internationalization extension in X11R4 and the
fact that HP is now using this extension. Emacs assumes that the
‘XLookupString’ function returns the same result regardless of the
<Meta> key state which is no longer necessarily true. Until Emacs is
fixed, the temporary kludge is to run this command after each time the X
server is started but preferably before any xterm clients are:
xmodmap -e 'remove mod1 = Mode_switch'
This will disable the use of the extra keysyms systemwide, which may
be undesirable if you actually intend to use them.