4.2 Terminology
Icon. A picture that stands for a thing: a program, a file, a kind of file, a directory. In this chapter an icon is always referred to by its identifier, and the picture is whatever the theme chain gives that identifier.
Identifier. The name of an icon: a short string in the form of §4.3.
generic, inode-directory and dev.peios.gxwi.hello are identifiers.
Theme. A directory holding one picture per identifier it provides, in the form of §4.4. A theme provides an identifier if the directory holds a file named for it.
Base theme. The theme every system has, on which every other stands. It is where a program's own icon is installed, and it provides every identifier of §4.A.
Chain. The ordered list of themes a consumer looks in. The chain is the system's, not the consumer's: it is set as §4.4 says, and it always ends in the base theme.
Subject. The thing a consumer wants an icon for: a path on the filesystem, usually. §4.5 gives the rules for a path; a specification that gives icons to other kinds of subject says how they yield an identifier.
Source. One place an identifier for a subject may come from: the file's extended attribute, the section a program carries, the file's name, the file's type. §4.5 lists the sources and the order they are consulted in.
Terms defined in PCDS (security descriptor) and in the Peios Kernel TRM (extended attribute) are used with the same meaning and are not redefined. Media type is used as RFC 6838 defines it.