Checklist

• Are you running the latest version? : 3.2.3
• Have you include sample input?
• Have you include actual output?
• Have you include expected output?
• Have you checked if you are using correct configuration?
• Did you try online tool?
• Did you bookmarked the repository for further updates? ;)

Input data

When I run the following code :

require('fast-xml-parser').validate(`<?xml version="1.0" encoding="UTF-8" standalone="yes"?><h1 a="fo'a"></h1>`)

I get :

{ err:
   { code: 'InvalidAttr',
     msg: 'Attributes for h1 have open quote' } }

Online, with the same input data, the error doesn't appear, but I think you might be using parse instead of validate (which also works locally)

I would expect the result to be a validationsuccess (return true)

It is allowed to have the single quote character if using double quotes as the delimiters (see https://stackoverflow.com/a/866894/1993501)