Assertion:
If no WIDTH attribute is set for a MARQUEE element, it behaves like a
block-level element (linebreak before and after) and occupies 100% of the containing
element/window width. If a width is set, it behaves like an in-line element.
Basic MARQUEE element, no width:
filler text
filler text
Basic MARQUEE element, width=500:
filler text
filler text