Is there a simple way to check if the string passed into the
LinkButton.label is a full URL (like protocol://server/page)?
or do I have to use "match" to check if the string matches a
regex to the URL?
You could create your own validator class that uses REGEX to
parse the URL to ensure it is valid. I wonder if you could use
try/catch or the result of calls to the URL to detect the error
pages you would receive if the URL is not valid.