You can use just about any HTML tag without a problem. You can add HTML if there is no TWiki equivalent, for example, write <strike>deleted text</strike> to get deleted text.
There are a few usability and technical considerations to keep in mind:
On collaboration pages, it's better not to use HTML, but to use TWiki shorthand instead - this keeps the text uncluttered and easy to edit.
Script tags may be filtered out, at the discretion of your TWiki administrator.
Recommendations when pasting HTML from other sources:
Copy only text between <body> and </body> tags.
Remove all empty lines. TWiki inserts <p /> paragraph tags on empty lines, which causes problems if done between HTML tags that do not allow paragraph tags, like for example between table tags.
Remove leading spaces. TWiki might interpret some text as lists.
Do not span a tag over more than one line. TWiki requires that the opening and closing angle brackets - <...> - of an HTML tag are on the same line, or the tag will be broken.
In your HTML editing program, save without hard line breaks on text wrap.
TWiki converts shorthand notation to HTML for display. To copy a fully marked-up page, simply view the source in your browser and save the contents. If you need to save HTML frequently, you may want to check out TWiki:Plugins/PublishAddOn.