For creating custom themes, see the Theme Development page

For creating custom extensions, see the Extension Development page

shm-* CSS classes are for javascript to hook into; if you're customising themes, be careful with these, and avoid styling them, eg:

• shm-thumb = outermost element of a thumbnail
  • data-tags
  • data-post-id
• shm-toggler = click this to toggle elements that match the selector
  • data-toggle-sel
• shm-unlocker = click this to unlock elements that match the selector
  • data-unlock-sel
• shm-clink = a link to a comment, flash the target element when clicked
  • data-clink-sel

Please tell me if those docs are lacking in any way, so that they can be improved for the next person who uses them