XAML, XUL, and XHTML Overlap
The greatest overlap between XAML and other standards lies in its support for concepts drawn from HTML/XHTML. The similarities between XAML and HTML are numerous. Overlap with HTML is not limited to XAML, of course. The other well-known XML GUI dialect—Mozilla's XUL—also overlaps with XHTML. Finally, both XAML and XUL overlap in places that XHTML doesn't even include. XHTML and XUL can be combined in one document (at least in Mozilla browsers). Such a combination is a rough analog for non-Web uses of XAML. In fact, Mozilla's XUL alone is a rough analog for some uses of XAML.

Table 2 shows a number of XAML tags that closely match standard XHTML tags, as well as the equivalent XUL tags, when available.

Table 2. XAML tags that duplicate XHTML and XUL functionality.

XAML Tag	XHTML tag	XUL tag
Audio	embed, object
Block	div
Break	br
Button	button	button
Cell	cell
CheckBox	input type="checkbox"	checkbox
Column	th	column listcol treecol
ComboBox	select	menupopup listbox
ComboBoxItem	option	menuitem listitem
Document	body
Footer	tfooter
Frame	frame, iframe	iframe
Header	theader	listheader treeheader
Heading	h1, h2, h3, h4, h5, h6	caption
HyperLink	a
Image	img	image
LineBreak	br
List	ul, ol
Listbox	select	listbox
ListElementItem		listcell treecell
ListItem	option	listitem treeitem
Menu	select	menu menulist
MenuItem	option	menuitem
Note	blockquote
Paragraph	p	description
RadioButton	input type="radio"	radio
RadioButtonList	input type="radio name="?"	radiogroup
Section	section	description
Table	table	grid
Text	input type="text"	textbox
TextBox	textbox	textbox multiline="true"
Video	embed, object

Table 2 contains a bewildering array of tags, but taken together, they really constitute nothing more than support for most of the basic HTML content and form widgets that are already routine in ordinary Web applications. XUL overlaps XHTML less that XAML does because XUL attempts to separate itself from XHTML. It's not trying to be a drop-in replacement, as XAML is.

One thing I do like about XAML compared with HTML is the increased freedom from the publishing-derived features of HTML. XAML frees you from h1 tags, code tags and a host of other miscellaneous niche tags used infrequently in HTML. For practical purposes, these tags act as little more than style information in modern HTML documents.

HTML is also a poor GUI for applications, despite the popularity of the Web. Both XAML and XUL go a long way towards rectifying that problem. You could re-write your Web applications in XAML and they'd look better than the HTML originals, if only XAML had better CSS support. There's that CSS issue again.