Two XSL files with import statements that import each other, cause the XML validation in the XML editor to enter a loop until the memory is consumed.  No 
way to validate those files or to cancel the validation.  Test files below:

=========  FILE: teststyle2.xsl ==================
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
    <xsl:import href="./teststyle1.xsl"/>
    <xsl:template match="/">
        <xsl:text>Teststyle 2</xsl:text>
    </xsl:template>
</xsl:stylesheet>

=========  FILE: teststyle1.xsl ==================
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
    <xsl:import href="./teststyle2.xsl"/>
    <xsl:template match="/">
       <xsl:text>Teststyle 1</xsl:text>
    </xsl:template>
</xsl:stylesheet>