Comment 1 for bug 1849229

This ticket was originally filed against Beautiful Soup: https://bugs.launchpad.net/beautifulsoup/+bug/1849211

The HTML spec defines tag names and attribute values as case-insensitive (http://w3c.github.io/html-reference/documents.html#case-insensitivity), so lxml's behavior is correct, but it might make sense to allow this as an option.