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To define a way to new span style you can apply styles to less than a paragraph without some sort of hackish work text selection, it must include the font-family property because that's how FogBugz finds it to include it in the templateFont menu. I've opened a case It needs to investigate this a bit know the difference between those fonts and will update herecustom sizes, which are put in the font size menu (they need to include the "font-size" property)
This blog post describes how to define custom styles in your wiki template.