Appendix B. HTTP Status Codes
You can find a detailed explanation of each status code in RFC 2616 (Hypertext Transfer Protocol—HTTP/1.1) at http://www.rfc-editor.org.
B.1. 100s: Informational
If an LWP request gets either of these rarely used codes, $response->is_info will be true. For all other status codes, $response->is_info will be false.
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