xpath find if node exists

Question

Using a xpath query how do you find if a node (tag) exists at all?

For example if I needed to make sure a website page has the correct basic structure like /html/body and /html/head/title

Answer 1

Maybe it's better to use XML Schema with obligatory elements indication? So check that a document uses it or not.

Answer 2

<xsl:if test="xpath-expression">...</xsl:if>

so for example

<xsl:if test="/html/body">body node exists</xsl:if>
<xsl:if test="not(/html/body)">body node missing</xsl:if>

Answer 3

A variation when using xpath in Java using count():

int numberofbodies = Integer.parseInt((String) xPath.evaluate("count(/html/body)", doc));
if( numberofbodies==0) {
    // body node missing
}

Answer 4

Try boolean(path-to-node)