Twine's engine is largely based on TiddlyWiki. The standard formatting codes are all TiddlyWiki syntax. Having a closer look at the code, though, I discovered a few other TiddlyWiki formatting codes are present in Jonah and Sugarcane - most interesting being Inline CSS, which ostensibly lets you apply inline styles around passage text. All you have to do is type "@@", then list CSS style attributes separated and terminated with semicolons, then put the passage text (including any other formatting and macros) ending with another "@@".

However, in the stable Twine versions of Jonah and Sugarcane, it is bugged - it will not work unless you include this code in a script passage:

String.prototype.unDash = function()
{
	var s = this.split("-");
	if(s.length > 1)
		for(var t=1; t < s.length; t++)
			s[t] = s[t].substr(0,1).toUpperCase() + s[t].substr(1);
	return s.join("");
}

If you include this code, you can use it. Here are some usage examples:

@@background-color:hsl(30,50%,50%);This text has an umber background.@@

@@color:gray;text-decoration:overline;This text is gray and has a vertical line over it.@@

@@letter-spacing: -2px;This text <<timedreplace 6>>and this macro<<endtimedreplace>> will be compressed.@@

@@text-shadow: 0.1em 0.1em #333;This text will have a gray shadow.@@

@@opacity:0.5;This text and this image [img[image.png]] will be translucent.@@

Now, as you know, there are methods to applying CSS to multiple passages easily. But, there are no doubt situations where you might need a few words in one passage to be a different colour, or in a different font, or anything the standard formatters don't cover. In those cases, this formatting syntax would be ideal.