In most of the CMS software I've worked with there is a simple method for identifying user-editable parts of a theme. In Concrete5, for example you can add something like:
<?php $a = new Area('Main Content'); $a->display($c); ?>
in any old
<div> and simply change
'Main Content' to whatever name is appropriate for that area. Glancing over the default Master Pages (as well as some others I've downloaded) that snippet seems to be some variant of
asp:ContentPlaceHolder in SharePoint's master pages, but there's one thing I can't seem to find documentation on...
Aside from the 30 or so "required" placeholders can "custom" placeholders be created to add additional user-editable areas to a theme? In other words, can I create a layout with, say, Twitter Bootstrap and then use
asp:ContentPlaceHolder to define the editable areas in the same way that I can use the above code snippet to "concrete-ize" a theme for C5? In addition to the "main" content area can I have other custom content areas?