The <tiles:insert> tag can lead to confusion because it can insert different things: pages, strings, definitions and attribute.
There is a particular confusion for the attribute, since some people could place it as they place definitions and pages, not remembering that attributes need to be filled.
<tiles:insert> could be split into:
<tiles:insertString> (not sure about it).
<tiles:attribute>: it has a different name pattern because attributes need to be "defined" and not "inserted".
And the message: