Commenting XML ... you have to write "<!--" and then "-->" ,if you have to write some large doc, and want it be well commented, you'll get really bored by typing four chars just to start comment block.
I was little frustrated by the fact there is no tool(well there is as a hint but i like key shortcuts) in my beloved NetBeans IDE to comment/uncomment whole block of text (like the Java editor has), so i wrote it down.
EDIT: It's useless "Ctrl-/" does the same for XML. See official short-cut list, its hidden in "Coding in Java" but works for many other file types.Download it for free right here:
It's simple, select text which you want to comment, right click for context menu and select "XML Comment" like the figure below shows.