Headers with multiple values

[g105b]

Headers with multiple values are separated with a comma/semicolon (need clarification).

https://github.com/php-fig/http-message/blob/master/docs/PSR7-Usage.md#getting-array-of-value-from-a-header-also-applies-to-request

When constructing the headers, should this be parsed? For example, the default accept header from Firefox: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8 - should this be split on the commas and added one by one?