How to decode a reserved escape character in a request URI on a web server?

Question

It is pretty clear that a web server has to decode any escaped unreserved character (such as alphanums, etc.) to do the URI comparison. For example, http://www.example

Answer 1

tl;dr:

Decode percent-encoded unreserved characters,
keep percent-encoded reserved characters.

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The URI standard is STD 66, which currently is RFC 3986.

Section 6 is about Normalization and Comparison, where section 6.2.2.2 explains what to do with percent-encoded octets:

These URIs should be normalized by decoding any percent-encoded octet that corresponds to an unreserved character […]

As explicitly stated in section 2 (bold emphasis mine):

• Unreserved characters:

  URIs that differ in the replacement of an unreserved character with its corresponding percent-encoded US-ASCII octet are equivalent

• Reserved characters:

  URIs that differ in the replacement of a reserved character with its corresponding percent-encoded octet are not equivalent.