What does this mean: onload_300; etc

I see these lines in the script I’m using. Can you tell me what they mean and what they do? Thanks

  <!--[onload_300;block=div;when [var.show_login_box]=1;comm]-->
 <!--[onload_337;block=div;when [var.show_login_box]!=1;comm]-->

Either they’re comments from something machine generated, or they’re some kind of templating/markup language that some code will interpret. On their own they mean absolutely nothing, just text in an HTML comment. They are not PHP code.