== In practice, there are multiple namespaces for URLs

In theory, the HTTP and URI/URL standards say that URLs are all in a
single namespace, as opposed to _GET_, _POST_, etc all using different
URL namespaces, where some URLs only exist for _POST_ and some only
exist for _GET_.

In practice, I believe that web traversal software should behave as if
there were two URL namespaces on websites: one for _GET_ and _HEAD_
requests, and a completely independent one for _POST_ requests.
Crawling software should not issue 'cross-namespace' URL requests,
because you simply can't assume that a URL that is valid in one can
even be *used* in the other.

This isn't very hard for _POST_ requests; not much software makes
them, and there's lots of things that make sending useful _POST_
requests off to URLs you've only seen in _GET_ contexts difficult. (In
theory you could try converting _GET_ requests with parameters into
_POST_ form requests with the same parameters, but I suspect this will
strike people as at least dangerous and questionable.)

Unfortunately I've seen at least one piece of software that went the
other way, issuing _GET_ requests for URLs that only appeared as the
target of _POST_ form actions. Since it tried this inside CSpace the
requests went down in flames, because I'm cautious about anything
involving _POST_ (and I get grumpy when things 'rattle the
doorknobs').

(The crawler in question was called _SBIder_, from sitesell.com, and
this behavior is one reason it is now listed in our
[[robots.txt|</robots.txt>]].)