Hi Mario,
Thank you for your reply.
I would have liked to be able to type some self-defined symbols such as ++ or :: and perform some custom functions.
For example, if I would type: ++ Custom block of text ++, then the HTML output would be <div style="background-color: #FFF">Custom block of text</div>, or wrapped in any other HTML blocks I choose.
Or perhaps preceding a line with :: could make a bullet point list with specific bullet symbols.
I could of course write a Javascript code that parses the text and produces the same effect but then the tiddler text will be permanently edited, which is different to how Markdown operates.
I hope this illustrated better what I was looking to achieve.