According to recomendations for creating a skin file on page 229 I enabled Intellisense using Tools->Options->Text Editor->File Extension, in Extension box typed skin and from Editor drop-down list choosed User Control Editor. I got Intellisense in skin file, but also got error message:
"There is no build provider registered for the extension ''. You can register one in the <compilation><buildProviders> section in machine.config or web.config. Make sure is has a BuildProviderAppliesToAttribute attribute which includes the value 'Web' or 'All'."
I found on Google solution how to get rid of error:
and inserted it in web.config:
<add extension="*" type="System.Web.Compilation.PageBuildProvider"/>
But it did not help me to get rid of error in skin file.