Case insensitive XPath contains() possible?

Case-insensitive contains

/html/body//text()[contains(translate(., 'EST', 'est'), 'test')]

This is for XPath 1.0. If your environment supports XPath 2.0, see here.

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Yes. Possible, but not beautiful.

/html/body//text()[
  contains(
    translate(., 'ABCDEFGHIJKLMNOPQRSTUVWXYZ', 'abcdefghijklmnopqrstuvwxyz'),
    'test'
  )
]

This would work for search strings where the alphabet is known beforehand. Add any accented characters you expect to see.

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If you can, mark the text that interests you with some other means, like enclosing it in a <span> that has a certain class while building the HTML. Such things are much easier to locate with XPath than substrings in the element text.

If that's not an option, you can let JavaScript (or any other host language that you are using to execute XPath) help you with building an dynamic XPath expression:

function xpathPrepare(xpath, searchString) {
  return xpath.replace("$u", searchString.toUpperCase())
              .replace("$l", searchString.toLowerCase())
              .replace("$s", searchString.toLowerCase());
}

xp = xpathPrepare("//text()[contains(translate(., '$u', '$l'), '$s')]", "Test");
// -> "//text()[contains(translate(., 'TEST', 'test'), 'test')]"

^{(Hat tip to @KirillPolishchuk's answer - of course you only need to translate those characters you're actually searching for.)}

This approach would work for any search string whatsoever, without requiring prior knowledge of the alphabet, which is a big plus.

Both of the methods above fail when search strings can contain single quotes, in which case things get more complicated.

XPath 2.0 Solutions

1. Use lower-case():

   /html/body//text()[contains(lower-case(.),'test')]

2. Use matches() regex matching with its case-insensitive flag:

   /html/body//text()[matches(.,'test', 'i')]