+<sect1>Z39.50 Protocol Support and Behavior
+
+<sect2>Initialization
+
+<p>
+During initialization, the server will negotiate to version 3 of the
+Z39.50 protocol, and the option bits for Search, Present, Scan,
+NamedResultSets, and concurrentOperations will be set, if requested by
+the client. The maximum PDU size is negotiated down to a maximum of
+1Mb by default.
+
+<sect2>Search
+
+<p>
+The supported query type are 1 and 101. All operators are currently
+supported except that only proximity units of type "word" are supported
+for the proximity operator. Queries can be arbitrarily complex. Named
+result sets are supported, and result sets can be used as operands with
+no limitations. Searches may span multiple databases.
+
+The server has full support for piggy-backed present requests (see
+also the following section).
+
+<bf/Use/ attributes are interpreted according to the attribute sets which
+have been loaded in the <tt/zebra.cfg/ file, and are matched against
+specific fields as specified in the <tt/.abs/ file which describes the
+profile of the records which have been loaded. If no <bf/Use/
+attribute is provided, a default of <bf/Any/ is assumed.
+
+If a <bf/Structure/ attribute of <bf/Phrase/ is used in conjunction with a
+<bf/Completeness/ attribute of <bf/Complete (Sub)field/, the term is
+matched against the contents of a phrase (long word) register, if one
+exists for the given <bf/Use/ attribute. If <bf/Structure/=<bf/Phrase/
+is used in conjunction with <bf/Incomplete Field/ - the default value
+for <bf/Completeness/, the search is directed against the normal word
+registers, but if the term contains multiple words, the term will only
+match if all of the words are found immediately adjacent, and in the
+given order. If the <bf/Structure/ attribute is <bf/Word List/,
+<bf/Free-form Text/, or <bf/Document Text/, the term is treated as a
+natural-language, relevance-ranked query.
+
+If the <bf/Relation/ attribute is <bf/Equals/ (default), the term is
+matched in a normal fashion (modulo truncation and processing of
+individual words, if required). If <bf/Relation/ is <bf/Less Than/,
+<bf/Less Than or Equal/, <bf/Greater than/, or <bf/Greater than or
+Equal/, the term is assumed to be numerical, and a standard regular
+expression is constructed to match the given expression. If
+<bf/Relation/ is <bf/Relevance/, the standard natural-language query
+processor is invoked.
+
+For the <bf/Truncation/ attribute, <bf/No Truncation/ is the default.
+<bf/Left Truncation/ is not supported. <bf/Process #/ is supported, as
+is <bf/Regxp-1/. <bf/Regxp-2/ enables the fault-tolerant (fuzzy)
+search. As a default, a single error (deletion, insertion,
+replacement) is accepted when terms are matched against the register
+contents.
+
+Zebra interprets queries in one the following ways:
+<descrip>
+<tag>1 Phrase search</tag>
+ Each token separated by white space is truncated according to the
+ value of truncation attribute. If the completeness attribute
+ is <bf/complete subfield/ the search is directed to the phrase
+ register. For other completeness attribute values the term is split
+ into tokens according to the white-space specification in the
+ character map. Only records in which each token exists in the order
+ specified are matched.
+<tag>2 Word search</tag>
+ The token is truncated according to the value of truncation attribute.
+ The completeness attribute is ignored.
+<tag>3 Ranked search</tag>
+ Each token separated by white space is truncated according to the value
+ of truncation attribute. The completenss attribute is ignored.
+<tag>4 Numeric relation</tag>
+ The token should consist of decimal digits. The integer is matched
+ against integers in the register according to the relation attribute.
+ The truncation - and the completenss attribute is ignored.
+<tag>5 Document identifier</tag>
+ The token consists of exactly one document identifier. The
+ truncation - and the completeness attribute is ignored.
+</descrip>
+
+For ranked searches the result sets are ranked and a score
+is associated with each record. All other result sets from the
+remaining four types are non-ranked.
+
+Combinations of the structure attribute and the relation attribute
+determine how the query is interpreted. The two following tables
+define how.
+
+<verb>
+ Structure Attribute (4)
+ none phrase(1) word(2) word list(6)
+
+ none 1 1 2 3
+ = (3) 1 1 2 3
+ < (1) 4 4 4 4
+Relation <= (2) 4 4 4 4
+Attribute >= (4) 4 4 4 4
+ (2) > (5) 4 4 4 4
+ <> (6) - - - -
+ rel (102) 3 3 3 3
+ other 1 1 2 3
+
+</verb>
+
+<verb>
+ Structure Attribute (4)
+ free-form- document- local- string
+ text text number
+ (105) (106) (107) (108)
+ none 3 3 5 1
+ = (3) 3 3 5 1
+ < (1) 4 4 5 4
+ Relation <= (2) 4 4 5 4
+ Attribute >= (4) 4 4 5 4
+ (2) > (5) 4 4 5 4
+ <> (6) - - 5 -
+ rel (102) 3 3 5 3
+ other 3 3 5 1
+
+</verb>
+
+<sect3>Regular expressions
+<p>
+
+Each term in a query is interpreted as a regular expression if
+the truncation value is either <bf/Regxp-1/ (102) or <bf/Regxp-2/ (103).
+Both query types follow the same syntax with the operands:
+<descrip>
+<tag/x/ Matches the character <it/x/.
+<tag/./ Matches any character.
+<tag><tt/[/..<tt/]/</tag> Matches the set of characters specified;
+ such as <tt/[abc]/ or <tt/[a-c]/.
+</descrip>
+and the operators:
+<descrip>
+<tag/x*/ Matches <it/x/ zero or more times. Priority: high.
+<tag/x+/ Matches <it/x/ one or more times. Priority: high.
+<tag/x?/ Matches <it/x/ once or twice. Priority: high.
+<tag/xy/ Matches <it/x/, then <it/y/. Priority: medium.
+<tag/x|y/ Matches either <it/x/ or <it/y/. Priority: low.
+</descrip>
+The order of evaluation may be changed by using parentheses.
+
+If the first character of the <bf/Regxp-2/ query is a plus character
+(<tt/+/) it marks the beginning of a section with non-standard
+specifiers. The next plus character marks the end of the section.
+Currently Zebra only supports one specifier, the error tolerance,
+which consists one digit.
+
+Since the plus operator is normally a suffix operator the addition to
+the query syntax doesn't violate the syntax for standard regular
+expressions.
+
+<sect3>Query examples
+<p>
+Phrase search for <bf/information retrieval/ in the title-register:
+<verb>
+ @attr 1=4 "information retrieval"
+</verb>
+
+Ranked search for the same thing:
+<verb>
+ @attr 1=4 @attr 2=102 "Information retrieval"
+</verb>
+
+Phrase search with a regular expression:
+<verb>
+ @attr 1=4 @attr 5=102 "informat.* retrieval"
+</verb>
+
+Ranked search with a regular expression:
+<verb>
+ @attr 1=4 @attr 5=102 @attr 2=102 "informat.* retrieval"
+</verb>
+
+<sect2>Present
+<p>
+The present facility is supported in a standard fashion. The requested
+record syntax is matched against the ones supported by the profile of
+each record retrieved. If no record syntax is given, SUTRS is the
+default. The requested element set name, again, is matched against any
+provided by the relevant record profiles.
+
+<sect2>Scan
+
+<p>
+The attribute combinations provided with the TermListAndStartPoint are
+processed in the same way as operands in a query (see above).
+Currently, only the term and the globalOccurrences are returned with
+the TermInfo structure.
+
+<sect2>Close
+
+<p>
+If a Close PDU is received, the server will respond with a Close PDU
+with reason=FINISHED, no matter which protocol version was negotiated
+during initialization. If the protocol version is 3 or more, the
+server will generate a Close PDU under certain circumstances,
+including a session timeout (60 minutes by default), and certain kinds of
+protocol errors. Once a Close PDU has been sent, the protocol
+association is considered broken, and the transport connection will be
+closed immediately upon receipt of further data, or following a short
+timeout.
+
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