Text selected in a message can be looked up on various websites and search engines by way of encoded URL strings. This functionality is the same in messages which are being composed, or which have been received.

At the bottom of the Edit menu are five entries:

• Google
• Dictionary
• Thesaurus
• Translate
• Wikipedia

The Dictionary and Thesaurus entries link to dictionary.com and thesaurus.com, respectively. (Both of which redirect to their respective subdomains at reference.com.)

The Translate feature automatically populates Yahoo's Babel Fish page with the selected term, at which point it is up to you to choose the desired languages.

Customizing

Each Reference Lookup engine has a pre-assigned keyboard shortcut. While only five entries are included by default, there’s actually space for a total of six. The shortcuts are mapped to Ctrl+3–5 and 7–9 (the last of these being unassigned by default). The reference lookup shortcuts are not contiguous because Ctrl+6 is assigned to the spell checker.

You can customize what each one does via hidden preference penelope.selectedTextURL1, penelope.selectedTextURL2, etc. (The hidden preferences dialogue is accessed via [Options/Prefs window] > Advanced > Config Editor.)

The format of a Reference Lookup entry is as follows:

• the name of the menu item
• a comma
• the URL to launch with "%s" (without the quotes) where the selected term should go

So the entry for Google looks like this:

Google,http://www.google.com/search?q=%s

And the entry for Wikipedia looks like this:

Wikipedia,http://en.wikipedia.org/wiki/%s

You should test the syntactic validity of your URL’s before adding them to your configuration.

The keyboard shortcuts are assigned by the application, and are not adjustable by the user.