String not accepted for $transform-before

[frank-steimke]

I want to use an xsl script as a preprocessor. When i use a customization layer that sets the value of $transform-before as a map with stylesheet-location, it does work,

But when i give the name of the stylesheet as a string value for the parameter $transform-before on the command line like this

java -jar $tng -o:article.html article.xml transform-before=../xsl/preprocessor.xsl

i get an error that Each $transform-preprocessed must be a string or a map:

Error at char 6 in expression in xsl:sequence/@select on line 137 column 98 of docbook.xsl:
  dbe:INVALID-TRANSFORM  Each $transform-preprocessed must be a string or a map
at variable vp:transforms on line 105 column 49 of docbook.xsl:
     invoked by global variable vp:transforms at https://cdn.docbook.org/release/xsltng/current/xslt/docbook.xsl#105
at template t:docbook on line 162 column 32 of docbook.xsl:
     invoked by xsl:call-template at https://cdn.docbook.org/release/xsltng/current/xslt/docbook.xsl#157
  In template rule with match="/" on line 146 of docbook.xsl
Each $transform-preprocessed must be a string or a map

Greetings, Frank