Assertion:
"The horizontal tab character (code position 9 in the HTML
document character set) must be interpreted as the smallest positive nonzero number
of spaces which will leave the number of characters so far on the line as a multiple of 8.
Documents should not contain tab characters as they are not supported consistently."
With this caveat, it is easy to see that the behavior of tabs may be VERY inconsistent
from browser to browser.
Simple PRE element, No TAB character used:
filler text
Preformatted content
12345678901234567890
filler text
Simple PRE element, TAB character (directly inserted in the text) located at
the beginning of the block. "<" points to the tab space:
filler text
<Preformatted content
12345678901234567890
filler text
Simple PRE element, TAB character (inserted using a character entity - 	)
located at the beginning of the block. "<" points to the tab space:
filler text
<Preformatted content
12345678901234567890
filler text
Simple PRE element, TAB character (directly inserted in the text) located after
some leading text. ">" and "<" point to the tab space:
filler text
pre> <Preformatted content
12345678901234567890
filler text