The document referenced by the src attribute may
be any valid document or any displayable object, including images and
multimedia. In particular, the referenced document may itself be
composed of one or more frames. The frames are displayed within the
referencing frame, providing yet another way of achieving complex
layouts using nested frames.
Since the source may be a complete document, all the features of
HTML/XHTML apply within a frame, including backgrounds and colors,
tables, fonts, and the like. Unfortunately, this also means that
multiple frames in a single browser window may conflict with each
other. Specifically, if each nested frame document (not a regular
HTML or XHTML document) has a different
<title> tag, the title of the overall
browser window will be the title of the most recently loaded frame
document. The easiest way to avoid this problem is to ensure that all
related frame documents use the same title.