Clarify cdx:device:certifications namespace

[Medical-Aegis]

The cdx:device:certifications has the following description:

cdx:device:certifications:<ISO-3166-1>	ISO-3166-1 alpha-2 country code of a certifying authority
cdx:device:certifications:<ISO-3166-1>:<AUTHORITY>	Abbreviation of the certifying authority (e.g. FCC, UL, and CE)
cdx:device:certifications:<ISO-3166-1>:<AUTHORITY>:id	Identifier for radio components.
cdx:device:certifications:<ISO-3166-1>:<AUTHORITY>:url	URL to certification details.

However, what's not very clear is if <ISO-3166-1> and <AUTHORITY> are part of the name or if the spec is saying those are just placeholders for the country code and certifying authority, in which case there are only 2 possible names (id and url) that certifications is describing.

So is it:

cdx:device:certifications:<ISO-3166-1> : US
cdx:device:certifications:<ISO-3166-1>:<AUTHORITY> : FCC
cdx:device:certifications:<ISO-3166-1>:<AUTHORITY>:id : 12345
cdx:device:certifications:<ISO-3166-1>:<AUTHORITY>:url : example.com

-OR-

cdx:device:certifications:US:FCC:id : 12345
cdx:device:certifications:US:FCC:url : example.com

[jkowalleck]

@Medical-Aegis

it is clearly the latter one: <FOO> is a placeholder for a class of values.
this would result in data like cdx:device:certifications:US:FCC:id : 12345.

would you mind pull requesting an improvement of the docs?