This appears to be a good excuse to hate on CSS Device Adaptation Module Level 1, let me quote from it so you understand the great sorrow I had when I needed to understand it:

This section is not normative. This section describes a mapping from the content attribute of the viewport <META> element, first implemented by Apple in the iPhone Safari browser, to the descriptors of the @viewport rule described in this specification.

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Below is an algorithm for parsing the content attribute of the <META> tag produced from testing Safari on the iPhone. The testing was done on an iPod touch running iPhone OS 4. The UA string of the browser: “Mozilla/5.0 (iPod; U; CPU iPhone OS 4_0 like Mac OS X; en-us) AppleWebKit/532.9 (KHTML, like Gecko) Version/4.0.5 Mobile/8A293 Safari/6531.22.7”. The pseudo code notation used is based on the notation used in [Algorithms].

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If a prefix of property-value can be converted to a number using strtod, the value will be that number. The remainder of the string is ignored.