<specifier, attribute> pairs.
These attributes
are the essential tokens and delimiters needed in scanning the
input index file. Default string constants are enclosed in
double quotes ("...") and character constants are
in single quotes ('x'). The user can override
the default value by specifying a specifier and a new attribute
in the format file or property sheet.
The attribute of keyword is self-explanatory;
arg_open and arg_close denote the argument opening and
closing delimiters, respectively.
The meanings of special operators such as level,
actual, and encap are described above.
The two range delimiters range_open and range_close are
used with the encap operator.
When range_open immediately follows encap
(i.e., \index{...|(...}),
it tells the index processor that an explicit range is starting.
Conversely range_close signals the closing of a range.
In our design, three or more successive page numbers are abbreviated as
a range implicitly. This implicit range formation can be turned
off if an indexed term represents logically distinct concepts in different
pages. When the implicit range is disabled, explicit page ranges
can be enforced by using the two range delimiters
range_open and range_close.
Therefore, it is possible to index an entire section or a large piece
of text related to a certain concept without having to insert an index
command in every single page.
The quote operator is used to escape symbols.
Thus \index{foo"@goo} means a sort key of foo@goo
rather than a sort key of foo" and an actual key of goo.
As an exception, quote, when preceded by escape (i.e.
\index{...\"...}), does not escape its succeeding letter.
This special case is included because \" is the umlaut
command in TEX. Requiring quote itself to be quoted
in this case (i.e. \"") is feasible but somewhat awkward;
quote and escape must be distinct.
A page number can be a composite of one or more fields
separated by the delimiter bound to page_compositor
(e.g., II-12 for page 12 of Chapter II).
This attribute allows the lexical analyzer to separate
these fields, simplifying the sorting of page numbers.