[Usability] Context sensitive buttons

[jim Pharis <binbrain gmail com>]

I need some clarification on a usability guideline in the HIG.

http://developer.gnome.org/projects/gup/hig/2.0/controls-buttons.html
Make invalid buttons insensitive, rather than popping up an error
message when the user clicks them.

Does this mean that an application can't dim a button but allow it to
be clickable? As an end user I might not understand why a button is
dimmed under certian circumstances. Am I
misinterpreting this guideline or is there another way to relay the
information to the user?

Check out the below link for justification for popping up the message
explaining why the button (or object) is context sensitive.

http://www.asktog.com/Bughouse/10MostPersistentBugs.html

Bug: Designers offer no way for users to discover why a given menu or
option has been dimmed (grayed out), nor how to turn it back on.

Class of error: Users are teased with options that they cannot access
without guessing what was in the designer's mind

Principle: Interfaces should be fully explorable. Users should never
have to guess at what unusual confluence of factors will enable them
to take advantage of a given capability of a website, application, or
system.

Proposed Fix: Make grayed-out objects clickable, revealing what has
caused the object to be dimmed and what the user can do about it.

Discussion: This design bug has hung around since the work at Xerox
PARC that laid the foundation for the Mac and the machines that
followed.

--
- Jim Pharis