When inserting the percent char twice, so that it appears in the PatternLayout output, a number format exception is thrown.

It does not prevent from using normally the PatternLayout.

trace:

ERROR in ch.qos.logback.core.joran.spi.Interpreter@131f71a - Exception in Action for tag <layout>8:14 java.lang.NumberFormatException: For input string: "% %"
java.lang.NumberFormatException: For input string: "% %"
at java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)
at java.lang.Integer.parseInt(Integer.java:447)
at java.lang.Integer.parseInt(Integer.java:497)
at ch.qos.logback.core.pattern.FormatInfo.valueOf(FormatInfo.java:70)
at ch.qos.logback.core.pattern.parser.Parser.T(Parser.java:84)
at ch.qos.logback.core.pattern.parser.Parser.E(Parser.java:51)
at ch.qos.logback.core.pattern.parser.Parser.Eopt(Parser.java:107)
at ch.qos.logback.core.pattern.parser.Parser.E(Parser.java:55)
at ch.qos.logback.core.pattern.parser.Parser.Eopt(Parser.java:107)
at ch.qos.logback.core.pattern.parser.Parser.E(Parser.java:55)
at ch.qos.logback.core.pattern.parser.Parser.Eopt(Parser.java:107)
at ch.qos.logback.core.pattern.parser.Parser.E(Parser.java:55)
at ch.qos.logback.core.pattern.parser.Parser.Eopt(Parser.java:107)
at ch.qos.logback.core.pattern.parser.Parser.E(Parser.java:55)
at ch.qos.logback.core.pattern.parser.Parser.Eopt(Parser.java:107)
at ch.qos.logback.core.pattern.parser.Parser.E(Parser.java:55)
at ch.qos.logback.core.pattern.parser.Parser.Eopt(Parser.java:107)
at ch.qos.logback.core.pattern.parser.Parser.E(Parser.java:55)
at ch.qos.logback.core.pattern.parser.Parser.Eopt(Parser.java:107)
at ch.qos.logback.core.pattern.parser.Parser.E(Parser.java:55)
at ch.qos.logback.core.pattern.parser.Parser.Eopt(Parser.java:107)
at ch.qos.logback.core.pattern.parser.Parser.E(Parser.java:55)
at ch.qos.logback.core.pattern.parser.Parser.parse(Parser.java:31)
at ch.qos.logback.core.pattern.PatternLayoutBase.start(PatternLayoutBase.java:76)
at ch.qos.logback.core.joran.action.AbstractLayoutAction.end(AbstractLayoutAction.java:75)
at ch.qos.logback.core.joran.spi.Interpreter.callEndAction(Interpreter.java:289)
at ch.qos.logback.core.joran.spi.Interpreter.endElement(Interpreter.java:152)
at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.endElement(AbstractSAXParser.java:633)
at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.scanEndElement(XMLNSDocumentScannerImpl.java:719)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDispatcher.dispatch(XMLDocumentFragmentScannerImpl.java:1685)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:368)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:834)
at com.sun.org.apache.xerces.internal.parsers.XML11Configuration.parse(XML11Configuration.java:764)
at com.sun.org.apache.xerces.internal.parsers.XMLParser.parse(XMLParser.java:148)
at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.parse(AbstractSAXParser.java:1242)
at javax.xml.parsers.SAXParser.parse(SAXParser.java:375)
at ch.qos.logback.core.joran.JoranConfiguratorBase.doConfigure(JoranConfiguratorBase.java:125)
at ch.qos.logback.core.joran.JoranConfiguratorBase.doConfigure(JoranConfiguratorBase.java:101)
at ch.qos.logback.core.joran.JoranConfiguratorBase.doConfigure(JoranConfiguratorBase.java:84)
at ch.qos.logback.core.joran.JoranConfiguratorBase.doConfigure(JoranConfiguratorBase.java:77)
at mainPackage.ConfigTester.main(ConfigTester.java:21)