XHTML is a myth. Don't use, don't worry about it.
I don't plan to: I only used XHTML 1.1 Strict when I started out because the validation tools were quite unforgiving by comparison to other flavours of HTML, which helped introduce a little discipline into my mark-up as a beginner. For example, I will continue to use quote marks on properties and other such XHTML requirements for consistency unless I find clear reasons not to. An exception, which you mention below, is content-type metatags where I would now use:
for instance, as opposed to:
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
Yep, I was guilty of that as you can see from the example immediately above: I think it might have been as late as 2010 before I actually read an in-depth exposition on the pointlessness of this exercise.
Pattern is an html 5 attribute to input. It hasn't been and will not be added to XHTML.
I understand this much and I should stress that, while I used to mark up pages in XHTML, I no longer do so. These days, I use the HTML5 DTD:
Thanks for pointing that out although the error was definitely due to the ampersand in the first pattern above: the page was declared as HTML5 and validated according to whatever currently passes for a standard. However, I have tried the mark-up without the 'closed' tag as you suggest and I'm pleased to note that it validates just as well. The parser would have accepted the XHTML mark-up for the purpose of backwards compatibility, which is another feature of HTML5. I will see about editing the mark-up for all 'closed' tags when I have had a careful look at the latest spec, which is, after all, an experimental feature.