So robg and I were discussing another hint submission of mine, one that robg couldn't understand because it referred to a menu he didn't have. After some back and forth, it turned out that the core of the suggestion for this new hint was actually on the site for a year, but buried at the bottom of a lengthy comment string.

The original hint covered how to enable the Debug menu in Safari, and dates back to 2003. With the advent of Safari 4, this command no longer worked. But somehow, I had a Debug menu and robg did not. The key is in a comment made by chleuasme, posted at the tail end of the comment thread on the original Enable the Safari debug menu hint. In the latest versions of Safari, the Debug menu is activated with a slightly different Terminal command:

defaults write com.apple.Safari IncludeInternalDebugMenu 1

As chleuasme also noted in their comment, this is publicly posted on the WebKit site.

[robg adds: I hadn't ever noticed the comment about how to enable the Debug menu in newer versions of Safari, and it's definitely worth sharing as a full hint. So thanks to chleuasme for finding it originally, and to Frederico for figuring out why I couldn't get the Debug menu to show up.]