Using the -a option
If the -a option is used, the name of the stylesheet is omitted. The source
document must contain a <?xml-stylesheet?> processing instruction
before the first element start tag; this processing instruction must have a
pseudo-attribute href that identifies the relative or absolute URL of the
stylsheet document, and a pseudo-attribute type whose value is text/xml,
application/xml, or text/xsl. For example:
It is also possible to refer to a stylesheet embedded within the source document,
provided it has an id attribute and the id attribute is
declared in the DTD as being of type ID. For example: