Okay, so here's what I'm trying to do but having a hell of a time figuring out.
I've got a website that uses the MemberPress plugin. All of those pages by default use the standard default template for each of their dynamically generated pages (i.e. thank you page, checkout page, account page, etc.). Furthermore, these pages are dynamically generated and can not be edited from the admin section to use whatever template you want.
So, all of the pages I am trying to change the template for have one thing in common, they all have a URL that has /register/ in it (i.e. www.mywebsite.com/register/page-name-here/.
Now I checked through all of the WordPress function references at the bottom of the page here... http://codex.wordpress.org/Function_Reference/is_page
I don't see anything I can use to determine if a page URL has /register/ in it but I would like to have some sort of code that I could put within my page.php default template that those pages use. The code would simply say something like...
if URL contains /register/ DO NOT include sidebar. Else include sidebar.
So in other words, the register pages would not include the sidebar and any other pages would include the sidebar. Make sense?