Error: The processing instruction target matching "[xX][mM][lL]" is not allowed

This error,

The processing instruction target matching "[xX][mM][lL]" is not allowed

occurs whenever I run an XSLT page that begins as follows:

<?xml version="1.0" encoding="windows-1256"?> 
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:include href="../header.xsl"/>
  <xsl:template match="/">
    <xsl:call-template name="pstyle"/>
    <xsl:call-template name="Validation"/>
    <xsl:variable name="strLang">
      <xsl:value-of select="//lang"/>
    </xsl:variable>
    <!-- ////////////// Page Title ///////////// -->
    <title>
        <xsl:value-of select="//ListStudentFinishedExam.Title"/>
    </title>

Note: I removed any leading spaces before the first line, but the error still occurs!

Xerces-based tools will emit the following error

The processing instruction target matching "[xX][mM][lL]" is not allowed.

when an XML declaration is encountered anywhere other than at the top of an XML file.

This is a valid diagnostic message; other XML parsers should issue a similar error message in this situation.

To correct the problem, check the following possibilities:

1. Some blank space or other visible content exists before the <?xml ?> declaration.

   Resolution: remove blank space or any other visible content before the XML declaration.

2. Some invisible content exists before the <?xml ?> declaration. Most commonly this is a Byte Order Mark (BOM).

   Resolution: Remove the BOM using techniques such as those suggested by the W3C page on the BOM in HTML.

3. A stray <?xml ?> declaration exists within the XML content. This can happen when XML files are combined programmatically or via cut-and-paste. There can only be one <?xml ?> declaration in an XML file, and it can only be at the top.

   Resolution: Search for <?xml in a case-insensitive manner, and remove all but the top XML declaration from the file.

Reason for me is 2 of following code in one xml

<?xml version="1.0" encoding="utf-8"?>

Check if you have this line repeated in your XML file

<?xml version="1.0" encoding="utf-8"?>

There was auto generated Copyright message in XML and a blank line before <resources> tag, once I removed it my build was successful.

Debug your XML file. Either there is space or added extra or fewer tags.

For better understanding build the project through the command line. Windows: gradlew build

In my case, AndroidManifest.xml has a blank space at the very first line

<Empty Row> // This Creates the issue 
<?xml version="1.0" encoding="utf-8"?>