You can go two ways with this in Eggplant. The first would be to script against the SUT’s browser the way a user might inspect for an HTML element. Something along the lines of[list]View -> Page SourceSearch for String[*]etc[/list:u]
Although completely doable this probably takes you into testing areas of the browser that are beyond the scope of what you really want to test (unless you are testing the browser itself).
NOTE: Safari actually has some great built in features for this by exposing the debug menu using this command
default write com.apple.safari IncludeDebugMenu -bool TRUE
However, sometimes an easier way to access this data is to pull it from the website directly in SenseTalk and inspect it in an Eggplant script. This is usually as easy as
put url ?http://www.somewhere.com/somepage.html? into
For more information about this refer to Chapter 15 of the SenseTalk reference manual.