Placement of the X<> entries

First, a definition. By "scope", I mean the part of the document that is deemed relevant to an index entry, and that may be extracted and shown in isolation by a processing or display tool. For example, perldoc -f considers the scope of a function to end at the beginning of the next =item, or at the end of the enclosing =over.

The X<> entries should be added at the end of a command or textblock paragraph (verbatim paragraphs are excluded). The scope of the index entry starts at the beginning of the paragraph to which it was attached; the end of the scope depends on the command type:

1) if the X<> is at the end of a textblock, the scope is that paragraph and zero or more verbatim paragraphs immediately following it.

2) if the X<> is at the end of a command paragraph, it depends on the type of command:

=head1, head2, etc.

The scope ends right before the next heading with equal or higher level. That is, a =head1 ends at the next =head1, and a =head2 ends at the next =head2 or =head1.

=item

The scope ends right before the next =item, or the =back that terminates the containing list. Note: "empty" items are not counted for terminating scopes, to allow for cases where multiple =items head a block of text. For example,

    =item function
    X<function>
    X<otherfunction>
    =item otherfunction
    C<function> and C<otherfunction> do the same thing,
    even if they    have different names...
    =item lemonade
    

Here the scope of the X<function> and X<otherfunction> entries starts with "=item function", and ends right before "=item lemonade".

3) other command paragraphs, such as =back, =over, =begin, =end, and =for should not be used for attaching X<> entries.

Content of the X<> entry.

• It should contain plain text without further formatting codes (with the possible exception of E<>).
• It should be in lowercase, unless caps are required due to case-sensitivity or correctness.
• Non-word characters are allowed, so one can list things like operators and special variables.
• Use of synonyms is encouraged, to make things easier to find.
• To be consistent, words should be normalized to the singular whenever possible. For example, use X<operator> instead of X<operators>.
• The use of a comma in an index entry has a special meaning: it separates levels of hierarchy (or namespaces), as a way of classifying entries in more specific ways. For example, "X<operator, logical>", or "X<operator, logical, xor>". This information may be used by processing programs to arrange the entries, or for listing results when a user searches for a namespace that contains several entries.
• There's no limitation as to the number of times that a given entry can appear in a document or collection of documents. That is, it is not an error to have X<whatever> appear twice in the same file.