html vs htm

Quick question --- I have replaced an old outdated site (not sure what platform was used to build it) with a new website using my Xara. So far I have desktop and mobile variant and will be adding an ipad variant. When working from Webmaster I noticed an html and htm link to the contact page and of course the older contact page had a "not found code" as it no longer exist.

Just trying to understand htm vs html I looked at my Xara files and realize that Xara only exports htm files. I thought that I had once noticed htm AND html files being uploaded (so I just thought html was the mobile version). Now I am only seeing htm files. Can you please explain the difference and if I did, at some point possibly have both file types or just possibly remembering it wrong.

If you change the Page Name for the home page to index.html all the other pages will publish as .html (Ignore the warning and click Rename)

If the browser finds two index files, one htm and the other html, it will automatically open the html page, even if the htm file is newer. At least it used to be this way. It may have changed.

Thank you gwpriester. So my files are obviously exporting out as htm. In Web Properties/Publish/Other web host settings I have the website url set as the main domain name (no htm or html added). So Xara automatically creates a sitemap. But according to WebMaster, the sitemap that was created is an html so I'm getting an error. Here's the error message "Your Sitemap appears to be an HTML page. Please use a supported sitemap format instead."

It doesn't really matter a great deal. As Gary says, browsers will look first for an index.html file. If they can't find that they look for an index.htm file and load that. The only time it will matter is that links to your old website might direct to xxxx.html which no longer exist. So I'd recommend deleting (or transferring) you old content and then publish anew using Gary's recommendation for using index.html

Of course on a new site there's no issue.

Thank you both for your help!!

Glad Egg and I could help.