When a browser's Accept request header says something like the following:
Accept: application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5
Does that mean that application/xml, application/xhtml+xml, and text/html all have a quality param of 0.9?
Or does it mean that application/xml and application/xhtml+xml have the default (q=1) and text/html has the q=0.9 param?
I'm assuming the former, but was hoping someone knew more definitively.
No, if the quality parameter is missing q=1.0 is assumed:
Each media-range MAY be followed by one or more accept-params, beginning with the "q" parameter for indicating a relative quality factor […] using the qvalue scale from 0 to 1 (section 3.9). The default value is q=1.
So the given value is to be interpreted as: “application/xml, application/xhtml+xml, and image/png are the preferred media types, but if they don’t exist, then send the text/html entity (text/html;q=0.9), and if that doesn’t exist, then send the text/plain entity (text/plain;q=0.8), and if that doesn’t exist, send an entity with any other media type (*/*;q=0.5).”
Verbally,this would be interpreted as "application/xml,application/xhtml+xml and image/png are the preferred media types,but if they do not exist,then send the text/html entity,and if that does not exist,send the text/plain entity,if that still does not exist,send an an entity with any other media type."
来源：https://stackoverflow.com/questions/5331452/http-accept-header-meaning