emacs -Q
M-x customize-option adaptive-file-first-line-regexp
 
The Hide Rest button has a tiny, tiny font. See attached screenshot.
 

In GNU Emacs 23.0.60.1 (i386-mingw-nt5.1.2600)
 of 2008-04-04 on LENNART-69DE564
Windowing system distributor `Microsoft Corp.', version 5.1.2600
configured using `configure --with-gcc (3.4) --no-opt --cflags -Ic:/g/include
-fno-crossjumping'