Is the protocol name in URLs case sensitive?

Question

Is hTTp://foo.com the same as Http://foo.COM?

I know that hostnames are not sensitive but path names and query parts are sensitive.

Answer 1

It is not sensitive in practice but in theory only lower case is allowed.

From RFC 1738

2.1. The main parts of URLs

A full BNF description of the URL syntax is given in Section 5.

In general, URLs are written as follows:

   :

A URL contains the name of the scheme being used () followed by a colon and then a string (the ) whose
interpretation depends on the scheme.

Scheme names consist of a sequence of characters. The lower case
letters "a"--"z", digits, and the characters plus ("+"), period
("."), and hyphen ("-") are allowed. For resiliency, programs
interpreting URLs should treat upper case letters as equivalent to lower case in scheme names (e.g., allow "HTTP" as well as "http").