To make sure all hypertext links are lowercase in HTML output:
[HTMLOptions]
; MakeFileHrefsLower = No (leave case unchanged) or Yes
MakeFileHrefsLower = Yes
MakeFileHrefsLower is set to Yes in system configuration file d2htm_config.ini. If you want DITA2Go to leave case alone in hypertext links, you must override this setting in a project or local configuration file.
MakeFileHrefsLower applies to hypertext links and interfile cross references. When you use the FileName property to name the section that contains the cross-reference destination, the setting applies also to cross references within the same file (see §43.3.3.3 Creating special paragraph formats to name output files).