Is array syntax using square brackets in URL query strings valid?

Question

Is it actually safe/valid to use multidimensional array synthax in the URL query string?

http://example.com?abc[]=123&abc[]=456

It seem

Answer 1

My understanding that square brackets are not first-class citizens anyway. Here is the quote: http://tools.ietf.org/html/rfc1738

Other characters are unsafe because gateways and other transport agents are known to sometimes modify such characters. These characters are "{", "}", "|", "\", "^", "~", "[", "]", and "`".