A new tag can be added into any text file including jsp, htm, html and xhtml.
It's very simple to do this. Open your JSP file and place the cursor in a place where you'd like to add a tag and then click that tag in the palette. In the Insert Tag window, that will appeared after that action, you can set the value of general and advanced attributes of the tag that you chose.
In the example below, the commandButton tag has been inserted.
if you place the cursor over any tag, a balloon tip is shown with all the "tag" attributes.
The cursor position after adding a tag into a file is specified by "|" symbol in the tag template on the right in the Palette Editor window.
Above you can see where the cursor position for HTML/Form/input is set. Thus, after adding this tag into your file the cursor will be in the attribute "type". Then, you can straight use the combination of buttons Ctrl + Space to inquire about a prompting.