TYPO3 Core

This TypoScript setup doesn't include external CSS:

page {
    includeCSSLibs {
        bootstrap = //netdna.bootstrapcdn.com/bootstrap/3.1.1/css/bootstrap.min.css
        bootstrap.external = 1
    }
}

This on with includeCSS work:

page {
    includeCSS {
        bootstrap = //netdna.bootstrapcdn.com/bootstrap/3.1.1/css/bootstrap.min.css
        bootstrap.external = 1
    }
}