Keymap that decodes input escape sequences.
This is used mainly for mapping ASCII function key sequences into
real Emacs function key events (symbols).
The `read-key-sequence' function replaces any subsequence bound by
`input-decode-map' with its binding. Contrary to `function-key-map',
this map applies its rebinding regardless of the presence of an ordinary
binding. So it is more like `key-translation-map' except that it applies
before `function-key-map' rather than after.
If the binding is a function, it is called with one argument (the prompt)
and its return value (a key sequence) is used.
The events that come from bindings in `input-decode-map' are not themselves looked up in `input-decode-map'.