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 .fi
 
 .SH
+9.7 BOOK INDEX
+
+.BR
+To make an index append to paragraph the book index term relates to it, using
+an equal sign and curly braces.
+
+.BR
+Currently two levels are provided, a main term and if needed a sub\-term.
+Sub\-terms are separated from the main term by a colon.
+
+
+.nf
+    Paragraph containing main term and sub\-term.
+.BR
+    ={Main term:sub\-term}
+.fi
+
+.BR
+The index syntax starts on a new line, but there should not be an empty line
+between paragraph and index markup.
+
+.BR
+The structure of the resulting index would be:
+
+
+.nf
+    Main term, 1
+.BR
+      sub\-term, 1
+.fi
+
+.BR
+Several terms may relate to a paragraph, they are separated by a semicolon. If
+the term refers to more than one paragraph, indicate the number of paragraphs.
+
+
+.nf
+    Paragraph containing main term, second term and sub\-term.
+.BR
+    ={first term; second term: sub\-term}
+.fi
+
+.BR
+The structure of the resulting index would be:
+
+
+.nf
+    First term, 1,
+.BR
+    Second term, 1,
+.BR
+      sub\-term, 1
+.fi
+
+.BR
+If multiple sub\-terms appear under one paragraph, they are separated under the
+main term heading from each other by a pipe symbol.
+
+
+.nf
+    Paragraph containing main term, second term and sub\-term.
+.BR
+    ={Main term:sub\-term+1|second sub\-term
+.BR
+    A paragraph that continues discussion of the first sub\-term
+.fi
+
+.BR
+The plus one in the example provided indicates the first sub\-term spans one
+additional paragraph. The logical structure of the resulting index would be:
+
+
+.nf
+    Main term, 1,
+.BR
+      sub\-term, 1\-3,
+.BR
+      second sub\-term, 1,
+.fi
+
+.SH
 10. COMPOSITE DOCUMENTS MARKUP
 .BR