What is _lpchecked="1" for in a form?

Question

I'm starting to do some web development and I was learning about forms and bumped into this field: _lpchecked = "1".

I found examples of form with this field in this StackOverflow question Large textinput makes http post fail or in this example page of the jQuery Formwizard plugin

Answer 1

This attribute is added by the LastPass browser extension, to store the fact that LastPass has checked that form for login fields.

It's not something that the page author would have consciously added to the page, it's down to the extensions that the user viewing the page has chosen to use.