Testing selector order in RSpec

Could someone point me to a reference that explains how I would test
the order of elements on an HTML page?

For example, in RSpec I would like to verify that the content of one
<p> element appears before the content of another.

response.should have_selector("p", :content => "Should appear first")
response.should have_selector("p", :content => "Should appear second")

The two lines above test that the 2 contents appear, but I don't know
how to test that the first content appears before the second.



Maybe use a regexp that has one and then the other, with .* between
them? Or find them, and make sure the indexes are in the right order?