Security guide suggests using invalid value for x-frame-options header

[t...@vestorly.com]

In the Default Headers section of the security guide, is suggests using ALLOWALL for the x-frame-options header:

X-Frame-Options: 'SAMEORIGIN' in Rails by default - allow framing on same domain. Set it to 'DENY' to deny framing at all or 'ALLOWALL' if you want to allow framing for all website.

According the discussion here points out, ALLOWALL is ignored by most browsers, and the correct way to get the expected behavior is to NOT set the header. Moreover, it's not a valid value according RFC 7034:

There are three different values for the header field.  These values
are mutually exclusive; that is, the header field MUST be set to
exactly one of the three values.

The valid values are: DENY, SAMEORIGIN, ALLOW-FROM.

So my question is: is there any reason to NOT update the doc? I'm happy to do it, I just wanted to verify first that there wasn't some explanation for why it should be left as-is.

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