So I download the source code, load up xsl_stylesheet.xml into Oxygen 11.2 and its complaining about multiple errors?

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Attribute "id" is required and must be specified for element type "reference".
Start location: 3:2
End location: 3:12

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Attribute "xml:id" must be declared for element type "reference".
Start location: 3:12
End location: 3:35

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Unexpected element "title". The content of the parent element type must match "(dl|parml|fig|syntaxdiagram|imagemap|image|lines| lq|note|hazardstatement|object|ol|p|pre|codeblock| msgblock|screen|simpletable|sl|table|ul|data|data-about|draft-comment|foreign|unknown|required-cleanup|bodydiv|example|section)*".
Start location: 5:8
End location: 5:13

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Element type "purpose" must be declared.
Start location: 6:8
End location: 6:15

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Element type "usage" must be declared.
Start location: 9:8
End location: 9:13

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Element type "element" must be declared.
Start location: 10:18
End location: 10:25

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Unexpected element "element". The content of the parent element type must match "(dl|parml|fig|syntaxdiagram|imagemap|image|lines| lq|note|hazardstatement|object|ol|pre|codeblock|ms gblock|screen|simpletable|sl|table|ul|boolean|cite |keyword|apiname|option|parmname|cmdname|msgnum|va rname|wintitle|ph|b|i|sup|sub|tt|u|codeph|synph|fi lepath|msgph|systemoutput|userinput|menucascade|ui control|q|term|abbreviated-form|tm|xref|state|data|data-about|foreign|unknown|draft-comment|fn|indextermref|indexterm|required-cleanup)".
Start location: 10:18
End location: 10:25

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Element type "attr" must be declared.
Start location: 12:26
End location: 12:30

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Element type "code" must be declared.
Start location: 15:17
End location: 15:21

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Unexpected element "code". The content of the parent element type must match "(dl|parml|fig|syntaxdiagram|imagemap|image|lines| lq|note|hazardstatement|object|ol|pre|codeblock|ms gblock|screen|simpletable|sl|table|ul|boolean|cite |keyword|apiname|option|parmname|cmdname|msgnum|va rname|wintitle|ph|b|i|sup|sub|tt|u|codeph|synph|fi lepath|msgph|systemoutput|userinput|menucascade|ui control|q|term|abbreviated-form|tm|xref|state|data|data-about|foreign|unknown|draft-comment|fn|indextermref|indexterm|required-cleanup)".
Start location: 15:17
End location: 15:21

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Element type "element" must be declared.
Start location: 17:31
End location: 17:38

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Element type "element" must be declared.
Start location: 18:17
End location: 18:24

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Element type "code" must be declared.
Start location: 19:29
End location: 19:33

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Element type "code" must be declared.
Start location: 20:27
End location: 20:31

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Element type "element" must be declared.
Start location: 21:18
End location: 21:25

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Unexpected element "element". The content of the parent element type must match "(dl|parml|fig|syntaxdiagram|imagemap|image|lines| lq|note|hazardstatement|object|ol|pre|codeblock|ms gblock|screen|simpletable|sl|table|ul|boolean|cite |keyword|apiname|option|parmname|cmdname|msgnum|va rname|wintitle|ph|b|i|sup|sub|tt|u|codeph|synph|fi lepath|msgph|systemoutput|userinput|menucascade|ui control|q|term|abbreviated-form|tm|xref|state|data|data-about|foreign|unknown|draft-comment|fn|indextermref|indexterm|required-cleanup)".
Start location: 21:18
End location: 21:25

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Element type "code" must be declared.
Start location: 24:17
End location: 24:21

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Unexpected element "code". The content of the parent element type must match "(dl|parml|fig|syntaxdiagram|imagemap|image|lines| lq|note|hazardstatement|object|ol|pre|codeblock|ms gblock|screen|simpletable|sl|table|ul|boolean|cite |keyword|apiname|option|parmname|cmdname|msgnum|va rname|wintitle|ph|b|i|sup|sub|tt|u|codeph|synph|fi lepath|msgph|systemoutput|userinput|menucascade|ui control|q|term|abbreviated-form|tm|xref|state|data|data-about|foreign|unknown|draft-comment|fn|indextermref|indexterm|required-cleanup)".
Start location: 24:17
End location: 24:21

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Element type "code" must be declared.
Start location: 25:41
End location: 25:45

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Element type "element" must be declared.
Start location: 27:17
End location: 27:24

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Unexpected element "element". The content of the parent element type must match "(dl|parml|fig|syntaxdiagram|imagemap|image|lines| lq|note|hazardstatement|object|ol|pre|codeblock|ms gblock|screen|simpletable|sl|table|ul|boolean|cite |keyword|apiname|option|parmname|cmdname|msgnum|va rname|wintitle|ph|b|i|sup|sub|tt|u|codeph|synph|fi lepath|msgph|systemoutput|userinput|menucascade|ui control|q|term|abbreviated-form|tm|xref|state|data|data-about|foreign|unknown|draft-comment|fn|indextermref|indexterm|required-cleanup)".
Start location: 27:17
End location: 27:24

SystemID: /home/sd/xslt book code/beginning xslt and xpath/ch01/xsl_stylesheet.xml
Engine name: Xerces
Severity: error
Description: Unexpected element "body". The content of the parent element type must match "(title,titlealts?,(abstract|shortdesc)?,prolog?,r efbody?,related-links?,(topic|concept|task|reference|glossentry|gl ossgroup)*)".
Start location: 4:5
End location: 4:9