Checkstyle config enforcing tabs but allowing leading spaces in text blocks.

checkstyle.xml

<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
		"-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
		"https://checkstyle.org/dtds/configuration_1_3.dtd">

<module name="Checker">

    <module name="SuppressWithPlainTextCommentFilter">
        <property name="offCommentFormat" value='=\s+"""'/>
        <property name="onCommentFormat" value='^\s+.*""";'/>
    </module>

    <module name="com.puppycrawl.tools.checkstyle.TreeWalker">
        <module name="SuppressWarningsHolder" />

        <module name="RegexpSinglelineJava">
            <property name="format" value="^\t* "/>
            <property name="message" value="Indent must use tab characters"/>
            <property name="ignoreComments" value="true"/>
        </module>
    </module>
</module>