The specification : string( <custom-ident> [ , [ first | start | last | first-except] ]? )

The second argument of the string() function doesn’t work. The second argument is one of the following keywords that indicates which value of the named string should be used: first | start | last | first-except

first-except actually works, but for now is the default argument. W3C specifications indicate that first is the default value.

The following graphic explains and resumes how the other keywords works:

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First

first: The value of the first assignment on the page is used. If there is no assignment on the page, the entry value is used. first is the default value.
CSS Generated Content for Paged Media Module, W3C Working Draft, 13 May 2014

Html file: first.html

Result: first-wrong.pdf

The result we should get: first-correct.pdf

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Start

start: If the element is the first element on the page, the value of the first assignment is used. Otherwise the entry value is used. The entry value may be empty if the element hasn’t yet appeared.
CSS Generated Content for Paged Media Module, W3C Working Draft, 13 May 2014

Html file: start.html

Result: start-wrong.pdf

The result we should get: start-correct.pdf

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Last

last: The exit value of the named string is used.
CSS Generated Content for Paged Media Module, W3C Working Draft, 13 May 2014

Html file: last.html

Result: last-wrong.pdf

The result we should get: last-correct.pdf