Here is a test with and expand and subexpand elements with html formatting in the Title Attribute:
[expand title="I am <b>bold</b>"]...[/expand]
However, this is not supported across all WordPress versions. Collapse-O-Matic version 1.3.6 offers some new placeholders to use as a work-around for WordPress installations that will not allow html in the title, swaptitle, startwrap, endwrap, excerpt and swapexcerpt attributes:
%(% = <
%)% = >
%{% = [
%}% = ]
[expand title="I am %(%b%)%bold%(%/b%)%"]...[/expand]
Collapse Commander
One benefit of using Collapse Commander is that all attributes are not processed through the shortcode attribute filters. This means that both HTML and Shortcodes are fully supported, without the need to further clutter the expand shortcode attributes with placeholders.