From a live site issue, we found that to be interoperable with Firefox and Chrome, we have to make the "url=" part of the content attribute optional. For example, sites will have the following syntax and expect to be "refreshed" to the specified URL:

<meta http-equiv="refresh" content="0;https://sourceforge.net/" />

Per the current spec text (steps 12-17 of the meta refresh processing steps (http://www.w3.org/html/wg/drafts/html/master/document-metadata.html#attr-meta-http-equiv-refresh)

     "If the character in input pointed to by position
     is a "U" (U+0055) character or a U+0075 LATIN SMALL LETTER U character
     (u), then advance position to the next character. Otherwise, jump to the
     last step.

     If the character in input pointed to by position
     is a "R" (U+0052) character or a U+0072 LATIN SMALL LETTER R character
     (r), then advance position to the next character. Otherwise, jump to the
     last step.

     If the character in input pointed to by position
     is s "L" (U+004C) character or a U+006C LATIN SMALL LETTER L character
     (l), then advance position to the next character. Otherwise, jump to the
     last step.

     Skip whitespace.

     If the character in input pointed to by position
     is a "=" (U+003D), then advance position to the next character.
     Otherwise, jump to the last step.

     Skip whitespace."

Jumping to the last step means that no url is parsed and the wrong thing happens. These steps need to be optional and still allow a URL following the number token to be parsed.