Protocols/MSNP/URL Encode

Named because its original use was to encode special characters in URLs, URL encoding enables the use of otherwise non-transmittable characters in the textual protocol stream. Non-encoded characters, except the percent sign, are transmitted as-is, while characters needing encoding (e.g. space, newline, the percent sign itself) are represented as %xx where xx is the hexadecimal value of the octet to be encoded.

See RFC3986:2.1 for more details.