For validating WildFly 9 standalone.xml using intellij IDEA.

misc.xml

<?xml version="1.0" encoding="UTF-8"?>
<project version="4">
  <component name="ClientPropertiesManager">
    <properties class="javax.swing.AbstractButton">
      <property name="hideActionText" class="java.lang.Boolean" />
    </properties>
    <properties class="javax.swing.JComponent">
      <property name="html.disable" class="java.lang.Boolean" />
    </properties>
    <properties class="javax.swing.JEditorPane">
      <property name="JEditorPane.w3cLengthUnits" class="java.lang.Boolean" />
      <property name="JEditorPane.honorDisplayProperties" class="java.lang.Boolean" />
      <property name="charset" class="java.lang.String" />
    </properties>
    <properties class="javax.swing.JList">
      <property name="List.isFileList" class="java.lang.Boolean" />
    </properties>
    <properties class="javax.swing.JPasswordField">
      <property name="JPasswordField.cutCopyAllowed" class="java.lang.Boolean" />
    </properties>
    <properties class="javax.swing.JSlider">
      <property name="Slider.paintThumbArrowShape" class="java.lang.Boolean" />
      <property name="JSlider.isFilled" class="java.lang.Boolean" />
    </properties>
    <properties class="javax.swing.JTable">
      <property name="Table.isFileList" class="java.lang.Boolean" />
      <property name="JTable.autoStartsEdit" class="java.lang.Boolean" />
      <property name="terminateEditOnFocusLost" class="java.lang.Boolean" />
    </properties>
    <properties class="javax.swing.JToolBar">
      <property name="JToolBar.isRollover" class="java.lang.Boolean" />
    </properties>
    <properties class="javax.swing.JTree">
      <property name="JTree.lineStyle" class="java.lang.String" />
    </properties>
    <properties class="javax.swing.text.JTextComponent">
      <property name="caretAspectRatio" class="java.lang.Double" />
      <property name="caretWidth" class="java.lang.Integer" />
    </properties>
  </component>
  <component name="ProjectLevelVcsManager" settingsEditedManually="false">
    <OptionsSetting value="true" id="Add" />
    <OptionsSetting value="true" id="Remove" />
    <OptionsSetting value="true" id="Checkout" />
    <OptionsSetting value="true" id="Update" />
    <OptionsSetting value="true" id="Status" />
    <OptionsSetting value="true" id="Edit" />
    <ConfirmationsSetting value="0" id="Add" />
    <ConfirmationsSetting value="0" id="Remove" />
  </component>
  <component name="ProjectResources">
    <resource url="urn:jboss:domain:batch:1.0" location="$PROJECT_DIR$/schema/wildfly-batch_1_0.xsd" />
    <resource url="urn:jboss:domain:bean-validation:1.0" location="$PROJECT_DIR$/schema/wildfly-bean-validation_1_0.xsd" />
    <resource url="urn:jboss:domain:datasources:3.0" location="$PROJECT_DIR$/schema/wildfly-datasources_3_0.xsd" />
    <resource url="urn:jboss:domain:deployment-scanner:2.0" location="$PROJECT_DIR$/schema/jboss-as-deployment-scanner_2_0.xsd" />
    <resource url="urn:jboss:domain:ee:3.0" location="$PROJECT_DIR$/schema/jboss-as-ee_3_0.xsd" />
    <resource url="urn:jboss:domain:ejb3:3.0" location="$PROJECT_DIR$/schema/wildfly-ejb3_3_0.xsd" />
    <resource url="urn:jboss:domain:infinispan:3.0" location="$PROJECT_DIR$/schema/jboss-as-infinispan_3_0.xsd" />
    <resource url="urn:jboss:domain:io:1.1" location="$PROJECT_DIR$/schema/wildfly-io_1_1.xsd" />
    <resource url="urn:jboss:domain:jaxrs:1.0" location="$PROJECT_DIR$/schema/jboss-as-jaxrs_1_0.xsd" />
    <resource url="urn:jboss:domain:jca:3.0" location="$PROJECT_DIR$/schema/wildfly-jca_3_0.xsd" />
    <resource url="urn:jboss:domain:jdr:1.0" location="$PROJECT_DIR$/schema/jboss-as-jdr_1_0.xsd" />
    <resource url="urn:jboss:domain:jmx:1.3" location="$PROJECT_DIR$/schema/jboss-as-jmx_1_3.xsd" />
    <resource url="urn:jboss:domain:jpa:1.1" location="$PROJECT_DIR$/schema/jboss-as-jpa_1_1.xsd" />
    <resource url="urn:jboss:domain:jsf:1.0" location="$PROJECT_DIR$/schema/jboss-as-jsf_1_0.xsd" />
    <resource url="urn:jboss:domain:logging:3.0" location="$PROJECT_DIR$/schema/jboss-as-logging_3_0.xsd" />
    <resource url="urn:jboss:domain:mail:2.0" location="$PROJECT_DIR$/schema/wildfly-mail_2_0.xsd" />
    <resource url="urn:jboss:domain:naming:2.0" location="$PROJECT_DIR$/schema/jboss-as-naming_2_0.xsd" />
    <resource url="urn:jboss:domain:pojo:1.0" location="$PROJECT_DIR$/schema/jboss-as-pojo_1_0.xsd" />
    <resource url="urn:jboss:domain:remoting:3.0" location="$PROJECT_DIR$/schema/wildfly-remoting_3_0.xsd" />
    <resource url="urn:jboss:domain:request-controller:1.0" location="$PROJECT_DIR$/schema/wildfly-request-controller_1_0.xsd" />
    <resource url="urn:jboss:domain:resource-adapters:3.0" location="$PROJECT_DIR$/schema/wildfly-resource-adapters_3_0.xsd" />
    <resource url="urn:jboss:domain:sar:1.0" location="$PROJECT_DIR$/schema/jboss-as-sar_1_0.xsd" />
    <resource url="urn:jboss:domain:security-manager:1.0" location="$PROJECT_DIR$/schema/wildfly-security-manager_1_0.xsd" />
    <resource url="urn:jboss:domain:security:1.2" location="$PROJECT_DIR$/schema/jboss-as-security_1_2.xsd" />
    <resource url="urn:jboss:domain:transactions:3.0" location="$PROJECT_DIR$/schema/jboss-as-txn_2_0.xsd" />
    <resource url="urn:jboss:domain:undertow:2.0" location="$PROJECT_DIR$/schema/wildfly-undertow_2_0.xsd" />
    <resource url="urn:jboss:domain:webservices:2.0" location="$PROJECT_DIR$/schema/jboss-as-webservices_2_0.xsd" />
    <resource url="urn:jboss:domain:weld:2.0" location="$PROJECT_DIR$/schema/jboss-as-weld_2_0.xsd" />
  </component>
  <component name="ProjectRootManager" version="2" languageLevel="JDK_1_6" default="false" assert-keyword="true" jdk-15="true" project-jdk-name="1.7" project-jdk-type="JavaSDK">
    <output url="file://$PROJECT_DIR$/out" />
  </component>
</project>

And here's how you use it, if you must.

1. Go download WildFly 9 and extract it somewhere convenient for you. Then again, if you're already editing a standalone.xml and already frustrated that almost every line has bold red validation "errors" on it, then you've already got WildFly somewhere. Well wherever it is, find its docs directory.
2. Copy the WildFly 9 docs/schema directory into your intellij project dir.
3. Immediately tell intellij IDEA to ignore that entire schema directory ('cuz you don't want to force everybody you're collaborating with to re-download a bunch of files to which they already have access - that would be rude and inefficient).
4. Find your project's .idea/misc.xml file and back it up somewhere just in case.
5. Copy the file above into your project's .idea/misc.xml.

Now go open a WildFly 9 standalone.xml (like the one that comes out of the tar in the first place) and see if most of that red crap has turned back to a friendlier, less alarming color.

"But wait!" you say... "There's still an error!"

Yeah, I'll bet it's still complaining to you about
<deployment-scanner path="deployments" relative-to="jboss.server.base.dir" scan-interval="5000" runtime-failure-causes-rollback="${jboss.deployment.scanner.rollback.on.failure:false}" />

Well I don't know why. But I think it's fine. Please ignore that.