Find text in webpage and email notification using applescript/automator

I don't have much experience in automator/applescript.

I need a script that searches a web page for a string of text, then if that text is found, it sends me an email. It should reload the page and search again about every 10 minutes. Ideally, this would all occur in the background, but I can live without that feature.

I found this thread from way back in 2011 which is exactly what I'm after, but I'm thinking something has changed over the years, because attempting to run it results in a syntax error.

Can anyone help with an update or explanation? Here is the original script:

on idle
          set pagURL to "http://page.url.com?whatever"
          if application "Safari" is not running then
                    quit
                    return
          end if
          tell application "Safari"
                    set URL of document 1 of window 1 to "http://your.web.address/"
                    delay 5

-- delay to let page load.  

-- there are more elegant ways of doing this using do javascript, but this will suffice.
                    if source of document 1 of window 1 contains "search text" then
                              my sendAMail()
                    end if
                    return 900 --fifteen minutes
          end tell
end idle

on sendAMail()
          tell application "Mail"
                    set theMess to make new outgoing message at end with properties {sender:"your name", subject:"some subject line", content:"The message you want to send to yourself", visible:true}
                    tell theMess
                               makenewto recipientat end of to recipientswith properties {address:"email@adress.com"}
                    end tell

-- send theMess
          end tell
end sendAMail

When I try to run the script in Automator, I get the following error: