When writing XSLT style sheets, it is very common to forget to close HTML elements. However, in XML, a P element must have an opening and a closing tag.
The following line is guaranteed to confuse the parser:
<xsl:template match="p"> <P><xsl:apply-templates/> </xsl:template>
Fortunately, the error message ("</P>" expected) is clear.
Similarly, <BR> is an empty tag. In XML, empty tags have the format <BR/>. Again, the error message ("</BR>" expected) is useful to pinpoint the problem.