Rebinding Escape

[PT]

In a special minor mode I want to allow the user to dismiss a popup help  
window quickly with the Escape key. I know it's prefix character, I only  
want to rebind it temporarily while the help window is shown.

I searched for a solution to override the default behavior, but found only  
an XEmacs-specific solution (setting meta-prefix-char to negative), but it  
didn't work. Esc still retains its old behavior.

Anyone has a better idea?

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