document character set
Technical term in computing and document processing; refers to the set of characters that can appear in a document, often defined by a standard or encoding.
In XML documents, specifying the document character set is important.
文字集合 is a broader term for any character set, while 文書文字集合 specifically refers to the character set used in a document context.
Compound of 文書 (document) + 文字 (character) + 集合 (set). A straightforward technical term.