If you have a multi-screen form and you want to write an LWP script to interact with this form just like a human, at some point, you must be able to return error's from script usage just as you would from interactive usage...

From what I can see, the biggest problem with this is how to have the script know the difference between normal HTML outuput of the screens and error alerts. Over the last 2 days, with much teeth-gnashing, I have run across or thought up a few different ways of providing "hints" to external LWP clients:

Comment the HTML

One thing you could do is edit all returned HTML with comments. Some comments would be instructions to the LWP client: 
<h3>Address Form</h3>


&lt;!-- BEGIN LWP: error &gt;
Your city and state do not match the indicated zip code. Please 
re-enter
&lt;!-- END LWP error &gt;

[download]

HTTP return codes

One other avenue is to use a predefined set of HTTP return codes and simply use the code to generate the error... but is it possible to "reserve" a subset of the HTTP return codes for each app's intended use?

A problem is that if a page had multiple problems, you can only return one status code and not alert the user to all problems with the input.

Parse the HTML

Admittedly a rough solution, but that's what brainstorming is all about. In my first incarnation of such a script that I wrote recently, I wrote a regexp to search for all text bracketed with  font color=red and used that as indication that the page had errors.

In reply to Providing Hints to LWP Applications by princepawn

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