DITA Validator for DITA-OT

Copyright (c) 2016 HERE Europe B.V.

See the LICENSE file in the root of this project for license details.

Introduction

The DITA Validator plug-in for DITA-OT is a structure, style and content checker for DITA documents. The plug-in returns information about the compliance of the document against a modifiable series of validator rules. The plug-in also supports standard XML validation

The plug-in supports two transtypes - it can either echo results to the command line or return a report in Schematron Validation Report Language (SVRL) format. More information about SVRL can be found at www.schematron.com

What Is Valid XML?

For any DITA publication to build successfully, all its files must contain valid DITA markup.

General XML validation rules require that:

• Documents are well formed.
• Documents contain only correctly encoded legal Unicode characters.
• None of the special syntax characters such as "<" and "&" appear except as markup delineators.
• The beginning and end tags must match exactly, unless tags are self-closing.
• A single root element such as <topic>, contains all the other elements.
• <topic> within a DITA document must conform to the topic.dtd Document Type Defintion

Validator compliant DITA

The DITA Validator extends the concept of XML validation to run a series of structure and style compliance rules. Sample rules include:

• Whether the source files for <image> and <codeblock> elements exist
• Whether conref attributes are linking to missing elements
• Whether every <section> or <fig> element in the document has a meaningful id
• Whether every <section> element has a title
• If an <xref> refers to a location on the web, both the scope="external" and format="html" attributes must be set
• Whether all id attributes are lower case and dash separated
• Whether any blacklisted words are found within the document.
• Whether the document will be unable to render as PDF due to empty <table> elements

Prerequisites

Requirements

The validator has been tested against DITA-OT 2.2.x. It is recommended that you upgrade to the latest version. Running the validator plug-in against earlier versions of DITA-OT will not work as it uses the newer getVariable template. To work with DITA-OT 1.8.5 this would need to be refactored to use getMessage

Installing DITA-OT

The DITA Validator is a plug-in for the DITA Open Toolkit.

• Install the DITA-OT distribution JAR file dependencies by running gradle install from your clone of the DITA-OT repository.

The required dependencies are installed to a local Maven repository in your home directory under .m2/repository/org/dita-ot/dost/.

• Run the Gradle distribution task to generate the plug-in distribution package:

./gradlew dist

The distribution ZIP file is generated under build/distributions.

Installation

Installing the Plug-in

• Run the plug-in installation command:

dita -install https://github.com/heremaps/com.here.validate.svrl/archive/v1.0.0.zip

The dita command line tool requires no additional configuration.

Usage

Validating a document from the Command line

A test document can be found within the plug-in at PATH_TO_DITA_OT/plugins/com.here.validate.svrl/sample

Creating an SVRL file

To create an SVRL file use the svrl transform.

• From a terminal prompt move to the directory holding the document to validate

• Clean the output directory (named "out" in the examples below), to ensure that the result from an old validation run is not present.

rm -rf ./out

• SVRL file creation (svrl) can be run like any other DITA-OT transform:

PATH_TO_DITA_OT/bin/dita -f svrl -o out -i document.ditamap

Once the command has run, an SVRL file is created

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<svrl:schematron-output>
	<active-pattern name="common-content-rules" role="content">
		<fired-rule context="title"/>
		<fired-rule context="p"/>
		<fired-rule context="section[id=&#34;good&#34;]"/>
		<fired-rule context="title"/>
		<fired-rule context="section[id=&#34;bad&#34;]"/>
		<fired-rule context="title"/>
		<failed-assert location="/topics/comment-fixme.dita" role="warning">
			<diagnostic-reference diagnostic="comment-fixme">Line 15: section[id="bad"] - [comment-fixme]
				Found 'FIXME' comments within the &lt;section&gt; element - fix as requested and delete the comment.
				FIXME 61) This comment requires action
			</diagnostic-reference>
		</failed-assert>
	</active-pattern>
</svrl:schematron-output>

Echoing results to the command line

To echo results to the command line use the svrl-echo transform.

• Clean the output directory, to ensure that the result from an old validation run is not present.

rm -rf ./out

• Document validation (svrl-echo) can be run like any other DITA-OT transform:

PATH_TO_DITA_OT/bin/dita -f svrl-echo -i document.ditamap

Once the command has run, all errors and warnings are echoed to the command line

[echo] [WARN]	 [/out/temp/dita/topics/comment-fixme.dita]
[echo]	 Line 15: section[id="bad"] - [comment-fixme]
[echo] Found 'FIXME' comments within the <section> element - fix as requested and delete the comment.
[echo]
[echo]	FIXME 61) This comment requires action
[echo]
[echo] Found 0 Errors 1 Warnings

Additionally, if an error occurs, the command will fail

[echo] [ERROR]	[/document.ditamap]
[echo]	 Line 89: topicref - [href-not-lower-case]
[echo] The value provided in href="topics/FILE-NOT-LOWER-CASE.dita" is invalid, allowed characters are: lowercase, a-z only, words separated by hyphens.
[echo]
[echo] Found 1 Errors 0 Warnings
Error: Errors detected during validation

Validating a document using Ant

An Ant build file is supplied in the same directory as the sample document. The main target can be seen below:

<dirname property="dita.dir" file="PATH_TO_DITA_OT"/>
<property name="args.input" value="PATH_TO_DITA_DOCUMENT/document.ditamap"/>
<path id="dita.ot.classpath">
	... etc..
</path>
<target name="validate">
	<java classname="org.apache.tools.ant.launch.Launcher" fork="true" failonerror="true" classpathref="dita.ot.classpath">
		<arg value="-Dargs.input=${args.input}"/>
		<arg value="-Ddita.dir=${dita.dir}"/>
		<arg value="-buildfile"/>
		<arg value="${dita.dir}/build.xml"/>
		<arg value="-Dgenerate-debug-attributes=false"/>
		<arg value="-Doutput.dir=out/svrl"/>
		<arg value="-Dtranstype=svrl-echo"/>
		<arg value="-Dargs.validate.blacklist=(kilo)?metre|colour|teh|seperate"/>
		<arg value="-Dargs.validate.check.case=Bluetooth|HTTP[S]? |ID|IoT|JSON|Java|Javadoc|JavaScript|XML"/>
		<arg value="-Dargs.validate.mode=default" />
		<arg value="-S"/>
		<arg value="-q"/>
	</java>
</target>

Parameter Reference

• args.validate.ignore.rules - Comma separated list of rules not to be enforced
• args.validate.blacklist - Comma separated list of words not to be present in the running text
• args.validate.check.case - Comma separated list of words which have a specified capitalization
• args.validate.mode - Validation reporting mode. The following values are supported:
  • strict - Outputs both warnings and errors. Fails on errors and warnings.
  • default - Outputs both warnings and errors. Fails on errors only
  • lax - Ignores all warnings and outputs errors only. Fails on Errors only
• svrl.customization.dir - Specifies the customization directory
• svrl.filter.file - Specifies the location of the XSL file used to filter the echo output

Adding New Validator Rules

This DITA-OT plug-in contains a common ruleset of general validator rules. The ruleset has been designed to be applicable to all documents created by all users. To add new custom rules (which only apply to your specific use case) you should create a separate custom validator plug-in which extends the base validator. See the sample Extended DITA Validator as an example of how to do this.

Altering the severity of a validator rule

The severity of a validator rule can be altered by amending entries in the cfg/rulesset/default.xml file The plug-in supports four severity levels:

• FATAL - Fatal rules will fail validation and cannot be overridden.
• ERROR - Error rules will fail validation. Errors can be overridden as described above.
• WARNING - Warning rules will display a warning on validation, but do not fail the validation. Warnings can also be individually overridden.
• INACTIVE - Inactive rules are not applied.

Ignoring Validator Rules

Removing validator rules globally

Rules can be made inactive by altering the severity (see above). Alternatively a rule can be commented out in the XSL.

To completely remove rules which do not apply to your document set, you can create a customized DITA-OT plug-in which extends the base validator. See the Extended DITA Validator as an example of how to do this.

Ignoring a validator rule throughout a document

Individual rules can be ignored by adding the args.validate.ignore.rules parameter to the command line. The value of the parameter should be a comma-delimited list of each rule-id to ignore.

For example to ignore the table-id-missing validation rule within a document you would run:

PATH_TO_DITA_OT/dita -f svrl-echo -i document.ditamap -Dargs.validate.ignore.rules=table-id-missing

Ignoring a specific instance of a validator rule

Specific instances of a rule can be ignored by adding a comment within the *.dita file. The comment should start with ignore-rule, and needs to be added at the location where the error is flagged.

...
<table platform="pdfonly" frame="none" >
	<!-- ignore-rule:table-id-missing -->
	<tgroup cols="1">
		<colspec colname="c1" colnum="1" colwidth="336pt"/>
		<tbody>
			<row>
				<entry>&#xA0;</entry>
			</row>
		</tbody>
	</tgroup>
</table>

Some rules such as FIXME and TODO in the running text need to be double escaped as shown below:

• Add a comment line with the text ignore-rule:running-text-* to ignore the issue flagged in the text below (no FIXMEs allowed in the running text)
• Add the comment-* to the list of ignored rules to ignore the fact that the comment itself fails an additional rule (no FIXMEs allowed in the comments)

<!--
	We want to display the text below which would usually
	result in a warning
-->
<p>
	<!-- ignore-rule:running-text-fixme,comment-fixme -->
	FIXME is usually banned in the running text.
</p>

Sample Document

A sample document can be found within the plug-in which can used to test validator rules. The document covers with positive and negative test cases. The sample document contains "broken" DITA which cannot be built as a PDF document - please use the html transform to read the contents or examine the *.dita files directly.

A complete list of rules covered by the DITA validator can be found below. The final <chapters> of the sample document contain a set of test DITA <topics>, each demonstrating a broken validation rule.

The <topic> files are sorted as follows:

• The base plug-in (com.here.validate.svrl) – this <chapter> contains a set of common validator rules applicable to all users. The rules are grouped thematically according to the name of the associated <active-pattern> within the XSL stylesheets of the plug-in and then are listed alphabetically by rule-id within the group. The following types of validation rules are supported: - style – Style rules enforce a standardized look and feel across DITA elements and ensure a better SEO and consistency. Alteration or removal of these rules should not affect the ability of DITA-OT to create a valid document. - structure – Structure rules offer an error reporting mechanism against fatal changes which would result in an invalid DITA document. If these rules are altered or removed, errors will not be caught up-front and DITA-OT will not be able to build a valid document. Examples include a conref link to a non-existent topic or an attempt to create a table containing no row elements. - content – These rules check the text within the DITA elements themselves, for example blacklisted words.
• The extended plug-in (com.here.validate.svrl.overrides) – This <chapter> shows how to modify, relax or remove existing validator rules and create additional custom validator rules. The custom rules are listed alphabetically by rule-id.

Note that extended rules will only be detected if the overrides transform from the Extended DITA Validator is used.

Validator Error Messages

The following tables list the validator error messages by type and message ID. Base DITA validator rules are in normal text. Rules in bold are examples of custom rules which can be detected if the overrides transform from the Extended DITA Validator is used.

Content Validation

Message ID	Message	Corrective Action/Comment
comment-fixme	Found 'FIXME' comments within the <{name}> element - fix as requested and delete the comment.	Replace the draft content with the correct information.
comment-todo	Found 'TODO' within the following text of the <{name}> element - fix as requested and delete the comment.	Replace the draft content with the correct information.
blacklisted-words	Words in the blacklist should not appear in the running text:	Remove the blacklisted words.
incorrect-capitalization	The word '{word}' is incorrectly capitalized in the following text:	The indicated word is not capitalized correctly. Fix the capitalization.
running-text-fixme	Found 'FIXME' comments in the following text in this <{name}> element - fix as requested and delete the comment.	Replace the draft content with the correct information.
running-text-lorem-ipsum	Found dummy text in this <{name}> element, remove or replace with valid content.	Replace the standard lorem ipsum filler text with the correct information.
running-text-todo	Found 'TODO' comments in the following text in this <{name}> element - fix as requested and delete the comment.	Replace the draft content with the correct information.

Style Validation

Message ID	Message	Corrective Action/Comment
codeblock-outputclass-missing	Always provide an outputclass attribute in <codeblock> elements (for example, add outputclass="language-javascript").	This outputclass attribute is used for decorating the HTML output to make code easier to read. If the content in the <codeblock> element is JSON use the key value pair outputclass="language-javascript". For more information on the <codeblock> element, see codeblock.
codeblock-scale-missing	Always provide a scale attribute in <codeblock> elements (for example, add scale="80").	This scale attribute reduces the size of the code text in the output to make it easier to read (the values are percent). We recommend you set the scale to 80 percent. For more information on the <codeblock> element, see codeblock.
conref-not-lower-case	The specification of conref="..." is invalid, allowed characters are: lower case, a-z only, words separated by hyphens.	The conref attribute is used for importing documentation segements reused across the document when the validator builds the document. For more information on using the conref attribute, see conref. When you get this error, the source file specified in the conref attribute references a file with an invalid name. For instance, if you define the conref attribute as follows <p conref="<InvalidFileName>#invalid-file-name/submission-note"> the file name does not comply with the file naming guidelines. - Only use lower case letters in a file name. - If a file name contains multiple words, use a hyphen to separate them, for example, overview-map.dita or request-map-report.dita. - The file type (and file extension) for all DITA XML files in the repository must be .dita or .ditamap. - Base the file name on the main topic title. If the title is Naming Conventions then the topic id should be naming-conventions and the file name should be naming-conventions.dita. - Do not include arbitrary strings to indicate the contents of the chapter, topic type, etc. - Do not include computer-generated text such as topic-2 or GUID-1234-5678-1234. - Do not use non-standard acronyms, for instance, border-xing instead of border-crossing.
element-blacklisted	The <name> element is not compliant with our subset of DITA documentation standards.	Custom Rule: While the DITA open standard supports a large number of elements, the extended validator only supports a subset of these elements in order to make the documents more consistent. Replace the rejected element with a supported element.
fig-id-invalid	id values must start with 'fig-' in all <fig> elements.	In order to assist with search engine optimization (SEO) of content, all figure elements must have an id.
fig-id-missing	Always provide an id value in <fig> elements.	In order to assist with search engine optimization (SEO) of content, all figure elements must have an id.
file-not-lower-case	Found file '...' with invalid name, allowed characters in file names are: lowercase, a-z only, words separated by hyphens.	In order to assist with search engine optimization (SEO) of content, file names must be lower case. Fix the name as appropriate.
href-not-lower-case	The value provided in href="..." is invalid, allowed characters are: lowercase, a-z only, words separated by hyphens.	The file specified in the href attribute does not comply with the file naming conventions. Fix the name as appropriate.
id-blacklisted	id attribute values must not use the word 'content'. Change the id value.	Custom Rule: Some delivery channels used to deliver content to customers may be configured to already use certain id values. Change the word content to another id. For more information on id attributes, see id.
id-not-lower-case	The ID value in id="..." is invalid, allowed characters are: lowercase, a-z only, words separated by hyphens.	In order to assist with search engine optimization (SEO) of content, id attributes must comply with the id conventions. Fix the name as appropriate. - Only use lower case letters in a file name. - If a file name contains multiple words, use a hyphen to separate them, for example, overview-map.dita or request-map-report.dita. - The file type (and file extension) for all DITA XML files in the repository must be .dita or .ditamap. - Base the file name on the main topic title. If the title is Naming Conventions then the topic ID should be naming-conventions and the file name should be naming-conventions.dita. - Do not include arbitrary strings to indicate the contents of the chapter, topic type, etc. - Do not include computer-generated text such as topic-2 or GUID-1234-5678-1234. For more information on id atrributes, see id.
image-file-type-not-supported	The value provided in href="..." specifies an unsupported file format (only *.jpg, *.jpeg or *.png are allowed). Change the format of the linked file.	The validator ensures that only *.jpg, *.jpeg or *.png format files are used in online HTML documents. Convert the image format to the correct format.
section-id-missing	Always provide an id attribute in <section> elements.	In order to assist with search engine optimization (SEO), all section elements must have an id.
table-id-missing	Always provide an id attribute in <table> elements.	In order to assist with search engine optimization (SEO), add an id to <table> elements. For more information on tables, see table.
topic-file-mismatch	The value specified in id="{name}" does not match the file name: {file_name}. Make sure the id value and the file name are the same.	In order to assist with search engine optimization (SEO) of content, the id for <topic> elements must be the same as the file name, which also ends up by the name of the HTML file. For more information on topics, see topic. For more information on element 'id`s', see id.
xref-no-format	Always provide a format attribute in <xref> elements, (for example, format="dita" or format="html").	Specify a value for the format attribute for <xref> elements. Examples of valid values include dita, html, and pdf. For more information on <xref> elements, see xref.

Structure Validation

Message ID	Message	Corrective Action/Comment
chapter-href-missing	Always provide an href attribute in <chapter> elements.	When you add a <chapter> element to a ditamap, you must specify a href="{file_name}" key/value pair that defines the content that appears on the chapter page in the PDF (and on the chapter landing page in HTML). Alternatively, you can define the following two attributes: navtitle="..." lockitle="yes". This approach has the effect of adding a title but not content on the chapter page/node. For more information on the <chapter> element, see chapter.
coderef-href-ref-file-not-found	The linked source file does not exist. Check the related folder for the missing file and make sure the file name is correct.	The <coderef> element is generally used for importing a source file when the validator builds the document. When you get this error, the reference cannot be resolved. Note that DITA does not allow you to reference files outside the root folder of the document. By default, these files should be in the source folder under the document root folder. For more information on the <coderef> element, see codeblock.
colspec-colnum-not-unique	The key/value pair colnum="..." is not unique. Make sure there are no duplicates.	In order for the validator to render table content properly, these key/value pairs must be unique. For instance, the following codeblock illustrates well-formated DITA that complies with this requirement. <colspec colnum="1"/><colspec colnum="2"/><colspec colnum="3"/> For more information on the <table> element, see table.
conref-external-file-not-found	The linked file does not exist. Check the related folder for the missing file and make sure the file name is correct.	The conref attribute is used for importing documentation segements reused across the document when the validator builds the document. For more information on using the conref attribute, see conref. When you get this error, the referenced file cannot be resolved. Note that DITA does not allow you to reference files outside the root folder of the document. By default, this kind of content should be in the includes.dita file.
conref-external-id-mismatch	The conref source <{name}> and the destination <{name}> are not the same type. Check to make sure the referenced elements are the same.	The conref attribute is used for importing documentation segements reused across the document when the validator builds the document. For more information on using the conref attribute, see conref. When you get this error, the referenced id in the source file specified in the conref attribute is an id for an element that is of a different type than the element with the conref attribute. DITA requires that conref attributes point at the same kind of element. For instance, <p conref="includes.dita#includes/submission-note"> needs to reference an element in the includes.dita file that is formatted as follows <p id="submission-note">CONTENT</p>.
conref-external-id-not-found	The referenced id does not exist in the source file. Make sure the ID value specified is correct.	The conref attribute is used for importing documentation segements reused across the document when the validator builds the document. For more information on using the conref attribute, see conref. When you get this error, the referenced id in the source file specified in the conref attribute cannot be resolved. For instance, if you define the conref attribute as follows <p conref="includes.dita#includes/submission-note"> and you get this error, then the includes.dita file does not have a <p> whose id is set to id="submission-note".
conref-external-path-not-found	The referenced path does not exist. Make sure the path is correct.	The conref attribute is used for importing documentation segements reused across the document when the validator builds the document. For more information on using the conref attribute, see conref. When you get this error, the source file specified in the conref attribute cannot be resolved. For instance, if you define the conref attribute as follows <p conref="includes.dita#includes/submission-note"> and you get this error, then the validator cannot find the includes.dita file. Note that DITA does not allow you to reference files outside the root folder of the document.
conref-external-path-mismatch	The conref source <{name}> and the destination <{name}> are not the same type. Make sure the path is correct.	The conref attribute is used for importing documentation segements reused across the document when the validator builds the document. For more information on using the conref attribute, see conref. When you get this error, the referenced id in the source file specified in the conref attribute is an id for an element that is of a different type than the element with the conref attribute. DITA requires that conref attributes point at the same kind of element. For instance, <p conref="includes.dita#includes/submission-note"> needs to reference an element in the includes.dita file that is formatted as follows <p id="submission-note">CONTENT</p>.
conref-internal-id-not-found	The referenced id does not exist in this file. Make sure the id value specified is correct.	The conref attribute is used for importing documentation segements reused across the document when the validator builds the document. For more information on using the conref attribute, see conref. When you get this error, the referenced id specified in the conref attribute cannot be resolved. For instance, if you define the conref attribute as follows <p conref="submission-note"> and you get this error, then the source file does not have a <p> whose id is set to id="submission-note".
conref-internal-path-mismatch	The conref source <{name}> and the destination <{name}> are not the same type. Make sure the path is correct.	The conref attribute is used for importing documentation segements reused across the document when the validator builds the document. For more information on using the conref attribute, see conref. When you get this error, the referenced id specified in the conref attribute is an ID for an element that is of a different type than the element with the conref attribute. DITA requires that conref attributes point at the same kind of element. For instance, <p conref="submission-note"> needs to reference an element that is formatted as follows <p id="submission-note">CONTENT</p>.
conref-internal-path-not-found	The referenced path does not exist in this file. Make sure the path is correct.	The conref attribute is used for importing documentation segements reused across the document when the validator builds the document. For more information on using the conref attribute, see conref. When you get this error, the value specified in the conref attribute cannot be resolved. For instance, if you define the conref attribute as follows <p conref="<file_name>#submission-note"> and you get this error, then the validator cannot resolve the path.
href-file-not-found	The file specified in href="..." does not exist. Check the related folder for the missing file and make sure the file name is correct.	The validator cannot find the file specified in the href attribute. Make sure the file is in the indicated path. Note that DITA does not allow you to reference files outside the root folder of the document.
id-not-unique	Found a duplicate ID with value '{name}', id values must be unique within a file. Change the id value.	DITA requires that all ids within a file must be unique. Change the id value. For more information on id attributes, see id.
image-href-ref-file-not-found	The linked image file does not exist. Check the graphics folder for the missing file and make sure the link and file name specified are correct.	The validator cannot find the file specified in the href attribute. Check the path to ensure the file is there.
image-product-filtered-not-included	Found <image product="...">. This results in an empty <fig> for other variants. Add additional product attributes for the missing ditaval filters.	Custom Rule: When skinning a document for various customers it is necessary to filter the images used. By placing all images in a single conref'd file it is easier to ensure that all images will be present for all customers. see ditavals.
list-all-li-filtered	Found only <li product="..."> elements in <ul>. This results in an empty <ul> for other variants. Either add additional product attributes for the ditaval filters or add <ul product="..."\> to the appropriate list elements.	The specified variant creation attributes result in a variant with a list without list items. Specify an additional variant attribute to ensure the list has items in all variants or remove the list entirely by specifiying the appropriate attributes. For more information on creating variants, see ditavals. For information on list items, see li.
table-all-rows-filtered	Found only <row product="..."\> elements in <tbody\>. This results in an empty <tbody> for other variants. Either add additional product attributes for the missing variants or add <table product="..."\> to the appropriate elements. The specified variant creation attributes result in a variant with a table without rows, which results in a broken PDF build.	Specify an additional variant attribute to ensure the table has rows in all variants or remove the table entirely by specifiying the appropriate attributes. For more information on creating variants, see ditavals. For more information on tables, see table.
tgroup-cols-colspec-mismatch	The number of {name} <colspec> elements defined do not match the parent <tgroup cols="..."\> attribute. Make sure the number of <colspec> elements corresponds with the cols value.	In order to generate PDFs correctly, the number of <colspec> elements must match the number in the <tgroup cols="..."> attribute. For more information on tables, see table.
tgroup-cols-entry-mismatch	The number of {name} <entry> elements found do not match the parent <tgroup cols="..."\> attribute. Make sure the number of <entry> elements corresponds with the cols value.	In order to generate PDFs correctly, the number of <entry> elements in a <row> element must match the number in the <tgroup cols="..."> attribute. For more information on tables, see table.
topicref-href-missing	Always provide an href attribute in <topicref> elements.	DITA uses the href attribute to specify connections between topicref elements and a file. Add an href attribute to the element and specify the appropriate value. For more information on <topicref> elements, see topicref.
xref-external-file-not-found	The file specified in <xref href="..."> does not exist. Check the related folder for the missing file and make sure the link and file name specified are correct.	When you get this error, the referenced file cannot be resolved. Note that DITA does not allow you to reference files outside the root folder of the document. Make sure the path exists. For more information on <xref> elements, see xref.
xref-external-id-not-found	The referenced id in <xref href="..."> does not exist. Make sure the id value specified is correct.	When you get this error, the validator cannot resolve the id in the target file. Note that DITA does not allow you to reference files outside the root folder of the document. Make sure the file exists and contains the id. For more information on <xref> elements, see xref.
xref-external-path-not-found	The referenced path in <xref href="..."> does not exist. Make sure the path specified is correct.	When you get this error, the validator cannot resolve the id in the target file. Note that DITA does not allow you to reference files outside the root folder of the document. Make sure the file exists and contains the id. For more information on <xref> elements, see xref.
xref-internal-id-not-found	The referenced ID in <xref href="..."> does not exist. Make sure the id value specified is correct.	When you get this error, the validator cannot resolve the id in the file. Make sure the file contains the id. For more information on <xref> elements, see xref.
xref-internal-path-not-found	The referenced path in <xref href="..."> does not exist. Make sure the path is correct.	When you get this error, the validator cannot resolve the provided path in the file. Make sure the file contains the path. For more information on <xref> elements, see xref.
xref-www-format-invalid	<xref href="..." format="dita"> The specified value points to an external file and cannot have the attribute key/value pair format="dita". Change the format value as appropriate (for example, format="html").	Specify a value for the format attribute for <xref> elements. Examples of valid values include dita, html, and pdf. For more information on <xref> elements, see xref.
xref-www-scope-invalid	<xref href="..."> The specified value points to an external file. Specify the attribute key/value pair scope="external".	The href attribute specifies a web page or similar target, which means the scope attribute must have the value external. Change the value as required. For more information on <xref> elements, see xref.