Minima and maxima

Min-width's initial value should be 0 (rather than ua-determined). There
is nothing particularly complicated about zero-width elements - I cannot
see anything intrinsically complicated about rendering:
<P style="width: 0">
Some text in a P element.
</P>
As:
Some
text
in
a
P
element.
, with the entirety of each word overflowing the containing block.

There is also a discrepancy with max-width and max-height as compared
with width and height.

<blockquote
cite="http://www.w3.org/TR/REC-CSS2/syndata.html#length-units">
Some properties allow negative length values, but this may complicate
the formatting model and there may be implementation-specific limits. If
a negative length value cannot be supported, it should be converted to
the nearest value that can be supported.
</blockquote>
<blockquote
cite="http://www.w3.org/TR/REC-CSS2/visudet.html#the-width-property">
Negative values for 'width' are illegal.
</blockquote>
So,
<p style="max-width: -100px">
Some text.
</p>
results in a width of 0 pixels (since negative max-widths are not
illegal and since the negative length will be clipped)
, whereas
<p style="width: -100px">
Some text.
</p>
is illegal, and hence will be ignored and treated as width: auto.

Equally for max-height.