Add function thematic_is_legacy_xhtml() to helpers.php
Use new thematic_is_legacy_xhtml() check to load legacy.php

Move loading of helper files earlier to the function is declared
Fix typos in comments in legacy.php
Switch .site-header to use <header> element

Add legacy filter to use <div> tags
Switch primary-menu to use <nav> element container

Add legacy filter to use <div> tags in xhtml mode
Switch widgets areas to use <aside> elements

Add legacy filters for using <div> tags and opening/closing <ul> list
Switch widgets to use <section> elements

Add legacy filters to use <li> elements in xhtml mode
Switch widgettitles to use <h1> elements

Add legacy filters to use <h3> elements in xhtml mode
Switch .site-footer to use <footer> element

Add legacy filter to use <div> tags in xhtml mode
Switch thematic_nav_above to use <nav> element

Add legacy override for <div> tag in xhtml mode
Switch thematic_nav_below to use <nav> element

Add legacy override for <div> tag in xhtml mode
Wrap thematic_postheader in <header> tags

Add css class .entry-header to <header>
Add legacy filter to remove the <header> tag in xhtml mode
Switch .entry-utility to use the <footer> element

Add legacy filter to use <div> tags in xhtml mode
Add html comment to closing tag of .entry-header
Change function name to thematic_navmenu_args_xhtml for consistency
Switch thematic_postheader_posttitle to always use <h1> headings

Add legacy filter for using h2 where appropriate in xhtml mode
Switch .page-link of wp_link_pages to use <nav> element

Add legacy filter to use <div> tags in xhtml mode
Define THEMATIC_MB constant for the unit tests
Switch the main loops to use <article> element

Add legacy functions for using <div> tags in xhtml mode
Group tests into groups, add test group for childtheme overrides