What is the /F function in PostScript?

When coding a PDF file, what is the /F function 开发者_如何学JAVAfor in a dictionary?

It depends entirely on the context. Any dictionary in a PDF file may contain any key and value. The PDF specification spells out all the standard dictionaries and their required contents, but part of the specification is that data should be carried through, even if it isn't part of the standard. For example, if I have a Page dictionary, I can put an F entry into it and expect it to be retained by spec compliant tools.

I know that the F key is found in the file specification dictionary, inline image objects, thread dictionaries, media play parameters dictionaries, media offset frame dictionaries, stream dictionaries, outline item dictionaries, reference dictionaries, annotation dictionaries, form field additional actions dictionaries and so on.