XML Validation

XML Syntax Errors

vscode-xml provides the capability to report XML syntax errors when the XML is not valid:

For many of the errors, you can use a Quick Fix (code action) to help you fix the XML:

Validation with a given grammar

You can validate your XML with a grammar (XSD, DTD). In order to do so, you must associate your XML document with a grammar. Once you have done this, you will benefit from:

XML validation based on the grammar.
XML completion based on the grammar.
XML hover based on the grammar in order to show the documentation.

If the xml.symbols.showReferencedGrammars setting is enabled, the method used to associate each grammar is listed in the document symbols. Please see the Show Referenced Grammars documentation for more information.

Validation with XSD grammar

In the following sections, we would like to validate the XML foo.xml file:

<foo>
  <bar />
</foo>

with the XSD foo.xsd file (in the same folder as foo.xml) :

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="https://www.w3.org/2001/XMLSchema">
  <xs:element name="foo">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="bar" />
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

in order to benefit from validation, completion, and hover based on the XSD:

To associate your XML document with an XSD grammar, you can use several strategies:

xsi:noNamespaceSchemaLocation
xsi:schemaLocation
xml-model with XSD processing instruction
XML catalog with XSD
XML file association

If you have an XML without an XSD, you can generate the XSD with a Quick Fix (code action):

The Quick Fix will generate the XSD file and associate the XML with the XSD using the chosen strategy.

xsi:noNamespaceSchemaLocation

To bind the XML file foo.xml with the XSD file foo.xsd, you can use the xsi:noNamespaceSchemaLocation strategy like this:

<foo
    xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
    xsi:noNamespaceSchemaLocation="foo.xsd">
  <bar />
</foo>

xsi:schemaLocation

The xsi:schemaLocation strategy is used when the XML document defines a namespace and the elements in the document are associated with that namespace:

<foo xmlns="https://foo"
    xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="https://foo foo.xsd">
  <bar />
</foo>

In this case, the corresponding XSD file defines targetNamespace="https://foo" in the root element of the XSD:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
    xmlns:xs="https://www.w3.org/2001/XMLSchema"
    elementFormDefault="qualified"
    targetNamespace="https://foo">
  <xs:element name="foo">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="bar" />
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

xml-model with XSD

To bind the XML file foo.xml to the XSD file foo.xsd, you can use xml-model processing instruction strategy like this:

<?xml-model href="foo.xsd" ?>
<foo>
  <bar />
</foo>

XML catalog with XSD

Using an XML catalog can be helpful when you wish to use elements from a namespace but don't want to set the real path of the XSD file for each XML document.

In other words you want to write this XML file:

<foo xmlns="https://foo" >
  <bar />
</foo>

and validate it with the foo.xsd XSD file:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
    xmlns:xs="https://www.w3.org/2001/XMLSchema"
    elementFormDefault="qualified"
    targetNamespace="https://foo">
  <xs:element name="foo">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="bar" />
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

To do this, you need to write an XML catalog, and an entry for the XSD. In this example, we'll name the catalog catalog.xml. The catalog looks like this:

<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog">

  <uri
      name="https://foo"
      uri="./foo.xsd" />

</catalog>

You must register your catalog.xml in the vscode settings.json like this:

"xml.catalogs": [
   "catalog.xml"
]

You can also register the catalog using its absolute path:

Windows	MacOS	Linux
`C:\\Users\\path\\to\\catalog.xml`	`/Users/path/to/catalog.xml`	`/home/path/to/catalog.xml`

Please note that you can declare your catalog path with file:/// if you need it.

Another useful option are the rewrite rules. Given the same xml as before but now with xmlns="https://foo.web/foo/types.xsd" can be adjusted to use a local types.xsd as follows:

<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog">

  <rewriteURI
      uriStartString="https://foo.web/foo/"
      rewritePrefix="./" />

</catalog>

XML file association with XSD

You can use the XML file association strategy to bind the XML file foo.xml with the XSD file foo.xsd by adding the following into your vscode settings.json:

"xml.fileAssociations": [
   {
       "pattern": "foo.xml",
       "systemId": "foo.xsd"
   }
]

Please note that you can use wildcards in the pattern (ex: foo*.xml):

"xml.fileAssociations": [
   {
       "pattern": "foo*.xml",
       "systemId": "foo.xsd"
   }
]

In this case, all XML files that start with foo and end with .xml will be associated with the XSD (foo1.xml, foo2.xml, etc)

You can also use the following three variables in either the pattern or systemId:

Variable	Meaning
${workspaceFolder}	The absolute path to root folder of the workspace that is currently open
${fileDirname}	The absolute path to the folder of the file that is currently opened
${fileBasenameNoExtension}	The current opened file's basename with no file extension

If one of the variables for an association can't be expanded (eg. because vscode is opened in rootless mode), the association is ignored. This feature is specific to the VSCode client.

Please note that if the XSD defines a targetNamespace="https://foo" like the following foo.xsd XSD file:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
    xmlns:xs="https://www.w3.org/2001/XMLSchema"
    elementFormDefault="qualified"
    targetNamespace="https://foo">
  <xs:element name="foo">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="bar" />
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

the following XML file association:

"xml.fileAssociations": [
   {
       "pattern": "foo*.xml",
       "systemId": "foo.xsd"
   }
]

will work with the following foo.xml XML file only if it declares the https://foo namespace:

<foo xmlns="https://foo" >
  <bar />
</foo>

Validation with DTD grammar

To associate your XML with a DTD grammar you can use several strategies:

DOCTYPE
xml-model with DTD processing instruction
XML catalog with DTD
XML file association with DTD

In the following sections we would like to validate the XML foo.xml file:

<foo>
  <bar />
</foo>

with the DTD foo.dtd file:

<!ELEMENT foo (bar)>
<!ELEMENT bar EMPTY>

Please note: this DTD file can be generated with the same Quick Fix which generates the XSD.

DOCTYPE

To bind the XML file foo.xml with the DTD file foo.dtd, you can use the DOCTYPE strategy like this:

<!DOCTYPE foo SYSTEM "foo.dtd">
<foo>
  <bar />
</foo>

xml-model with DTD

To bind XML file foo.xml with the DTD file foo.dtd, you can use xml-model processing instruction strategy like this:

<?xml-model href="foo.dtd" ?>
<foo>
  <bar />
</foo>

XML catalog with DTD

Using an XML catalog can be helpful when you wish to associate to a DTD using a PUBLIC declaration, but don't want to set the real path of the DTD file (SYSTEM).

In other words you want to write this XML file:

<!DOCTYPE foo PUBLIC "-//FOO" "XXXXXXXXXXXXXXX.dtd">
<foo>
  <bar />
</foo>

and validate it with this foo.dtd DTD file:

<!ELEMENT foo (bar)>
<!ELEMENT bar EMPTY>

The declared XXXXXXXXXXXXXXX.dtd in the DOCTYPE is a file which doesn't exist. The foo.dtd will be retrieved using the PUBLIC -//FOO.

To do this, you need to write an XML catalog, and an entry for the DTD. In this example, we'll name the catalog catalog.xml. The catalog looks like this:

<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog">

  <public
      publicId="-//FOO"
      uri="./foo.dtd" />

</catalog>

and in vscode settings.json you must register your catalog.xml like this:

"xml.catalogs": [
   "catalog.xml"
]

You can also register the catalog using its absolute path:

Windows	MacOS	Linux
`C:\\Users\\path\\to\\catalog.xml`	`/Users/path/to/catalog.xml`	`/home/path/to/catalog.xml`

XML file association with DTD

You can use the XML file association strategy to bind the XML file foo.xml with the DTD file foo.dtd by adding the following into your vscode settings.json:

"xml.fileAssociations": [
  {
      "pattern": "foo.xml",
      "systemId": "foo.dtd"
  }
]

Please note that you can use wildcards in the pattern (ex: foo*.xml):

"xml.fileAssociations": [
  {
      "pattern": "foo*.xml",
      "systemId": "foo.dtd"
  }
]

In this case, all XML files that start with foo and end with .xml will be associated with the DTD (foo1.xml, foo2.xml, etc)

You can also use the following three variables in either the pattern or systemId:

Variable	Meaning
${workspaceFolder}	The absolute path to root folder of the workspace that is currently open
${fileDirname}	The absolute path to the folder of the file that is currently opened
${fileBasenameNoExtension}	The current opened file's basename with no file extension

If one of the variables for an association can't be expanded (eg. because vscode is opened in rootless mode), the association is ignored. This feature is specific to the VSCode client.

Validation with RelaxNG grammar

See RelaxNG features

Other Validation Settings

Disallow Doc Type Declarations

If xml.validation.disallowDocTypeDeclaration is set to true (default is false), all Doc Type Declarations (DTD) will be marked as errors. The DOCTYPE is marked as an error regardless if the doctype is an internally declared or a reference to an external DTD. Standalone .dtd files are not marked as an error.

Here are some examples of files with xml.validation.disallowDocTypeDeclaration set to true:

Resolve External Entities

If xml.validation.resolveExternalEntities is set to true (default is false), then the value of external entities are resolved for validation. This means that the file referenced in the external entity declaration will be downloaded. The default is false due to the xml external entity attack.

In an untrusted workspace, this feature is disabled.

Demonstration of the different behaviour:

xml.validation.namespaces.enabled

The xml.validation.namespaces.enabled gives the capability to enable / disable the namespaces (prefix) validation. It can be configured with 3 values:

always: enable schema based validation.
never: disable schema based validation.
onNamespaceEncountered: enable namespaces validation only when the root element declares an xmlns namespace.

To understand the onNamespaceEncountered settings value, lets go through an example:

Create the XML foo.xml file:

<foo>
	<p:bar />
</foo>

In always you will have error, in onNamespaceEncountered you will have none error.

Declares a namespaces in the foo root element:

<foo xmlns="http:foo" >
	<p:bar />
</foo>

In onNamespaceEncountered you will see a prefix error.

xml.validation.schema.enabled

The xml.validation.schema.enabled gives the capability to enable / disable the validation based on XSD. It can be configured with 3 values:

always: enable schema based validation.
never: disable schema based validation.
onValidSchema: enable schema based validation only when the declared xsi:schemaLocation hint or xsi:noNamespaceSchemaLocation is valid for the root element.

To understand the onValidSchema settings value, lets go through an example:

Create the XML foo.xml file:

<foo xmlns="https://foo"
	xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="
		https://foo foo.xsd">
	<bar />
	<BAD_ELEMENT />
</foo>

Create the XSD foo.xsd file (in the same folder as foo.xml) :

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="https://www.w3.org/2001/XMLSchema">
  <xs:element name="foo">
    <xs:complexType>
      <xs:sequence>
        <xs:element name="bar" />
      </xs:sequence>
    </xs:complexType>
  </xs:element>
</xs:schema>

In the XML file, the BAD_ELEMENT is higlighted as an error. Update the xsi:schemaLocation with bad namespace hint

<foo>
...
	xsi:schemaLocation="
		https://bad-foo foo.xsd">
...
</foo>

In always you will have error, in onValidSchema you will have none error.

Now, update the xsi:schemaLocation with bad location hint

<foo>
...
	xsi:schemaLocation="
		https://foo bad-foo.xsd">
...
</foo>

In always you will have error, in onValidSchema you will have none error.

xml.validation.filters

XML validation filter gives you the capability to define validation rules for files matching a given pattern. For instance if you wish to disable validation for all files which have the *.myxml file extension, you must declare this filter in the settings.json:

"xml.validation.filters": [
   // Declaration of validation filter to disable validation for all *.myxml files.
   {
    "pattern": "**.myxml",
    "enabled": false
  }
]

You can use other validation settings (enabled, noGrammar, etc). For instance if you wish to remove the warning no grammar for all files which have the *.myxml file extension, you must declare this filter in the settings.json:

"xml.validation.filters": [
   // Declaration of validation filter to disable validation for all *.myxml files.
   {
    "pattern": "**.myxml",
    "noGrammar": "ignore"
  }
]

By default, vscode-xml uses this default validation filter:

"xml.validation.filters": [
  // Ignore no grammar hint and disable XSD validation for *.exsd Eclipse files.
  {
    "pattern": "**.exsd",
    "noGrammar": "ignore",
    "schema": {
      "enabled": "never"
    }    
  },
  // Ignore no grammar hint for Eclipse files like .project
  {
    "pattern": "**{.project,.classpath,plugin.xml,feature.xml,category.xml,.target,.product}",
    "noGrammar": "ignore"
  }
]

xml.validation.xInclude.enabled

The xml.validation.xInclude.enabled gives the capability to enable / disable the validation for XInclude. Defaults to false.

See XInclude features

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