Custom.master
System pages, such as forms and views. Used by all SharePoint 2013 and SharePoint Online SKUs.
Default.master
Site pages in publishing sites. Included in all SharePoint 2013 and SharePoint Online SKUs. Available when the publishing feature is activated.
Application.master
Some system pages, such as scope.aspx and keyword.aspx. Included in all SharePoint 2013 and SharePoint Online SKUs. Minimal.master
Available default master page option in all SharePoint 2013 SKUs.
Seattle.master
Available default master page option in all SharePoint 2013 and SharePoint Online SKUs.
Oslo.master
Available default master page option in all SharePoint 2013 and SharePoint Online SKUs.
Kyoto.master
A master page available in SharePoint Online.
Berlin.master
A master page available in SharePoint Online.
Lyon.master
A master page available in SharePoint Online.
Mysite15.master
OneDrive for Business sites (previously: My Site, personal sites, or OneDrive Pro sites).

The Literal content (' ') is actually an html non-breaking space that gets added when editing the page in SharePoint Designer for the first time
Remove the $nbsp; and save the page again to clear the error.