Will Sigil support the entire Unicode System?

Did searches and found nothing.

Notice that the XHTML files in Sigil have this opening XML tag:

<?xml version="1.0" encoding="utf-8"?>

Will Sigil support these opening tags?

<?xml version="1.0" encoding="utf-16"?>

<?xml version="1.0" encoding="utf-32"?>

When I tried using this tag:

<?xml version="1.0" encoding="utf-16"?>

the XHTML file saved, but it was completely goobly-doo with Asian ideograms instead of english latin characters. I have an Ebook project that would be fantastic if I could use UTF characters above the UTF-8. Otherwise, I do not look forward to making a bunch of PNGs of the characters I wish to use. But will if I have to... ...

Any help is much appreciated.

Thanks.

adeg