➜  src cat Test.java
public class Test {
    void m0() {
        String s = STR."x"; // expected violation
    }

    void m1() {
        String s = "x"; // actual violation
    }
}

➜  src cat config.xml 
<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
    "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
    "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">
<module name="Checker">
  <module name="TreeWalker">
    <module name="IllegalTokenText">
      <property name="format" value="x"/>
    </module>
  </module>
</module>

➜  src java -jar checkstyle-10.12.8-SNAPSHOT-all.jar -c config.xml Test.java
Exception in thread "main" java.lang.IllegalArgumentException: unknown TokenTypes value 'STRING_TEMPLATE_CONTENT'
        at com.puppycrawl.tools.checkstyle.utils.TokenUtil.getTokenId(TokenUtil.java:162)
        at com.puppycrawl.tools.checkstyle.TreeWalker.registerCheck(TreeWalker.java:215)
        at com.puppycrawl.tools.checkstyle.TreeWalker.setupChild(TreeWalker.java:133)
        at com.puppycrawl.tools.checkstyle.AbstractAutomaticBean.configure(AbstractAutomaticBean.java:207)
        at com.puppycrawl.tools.checkstyle.Checker.setupChild(Checker.java:481)
        at com.puppycrawl.tools.checkstyle.AbstractAutomaticBean.configure(AbstractAutomaticBean.java:207)
        at com.puppycrawl.tools.checkstyle.Main.runCheckstyle(Main.java:411)
        at com.puppycrawl.tools.checkstyle.Main.runCli(Main.java:338)
        at com.puppycrawl.tools.checkstyle.Main.execute(Main.java:195)
        at com.puppycrawl.tools.checkstyle.Main.main(Main.java:130)

➜  src java -jar checkstyle-10.12.8-SNAPSHOT-all.jar -c config.xml Test.java
Starting audit...
[ERROR] /home/nick/IdeaProjects/tester/src/Test.java:3:25: Token text matches the illegal pattern 'x'. [IllegalTokenText]
[ERROR] /home/nick/IdeaProjects/tester/src/Test.java:7:20: Token text matches the illegal pattern 'x'. [IllegalTokenText]
Audit done.
Checkstyle ends with 2 errors.