Unable to create an inline widget with nested editable span

[Libor Bus]

I am implementing a new widget which represents a link and allows user to enter link text and URL without any dialog. Its template looks as follows:

template:
    '<a href="" class="linkwidget"><span class="linkwidget-text">Content...</span>' +
    '<span class="linkwidget-info"> (<i class="icon-external-link"></i> <span class="linkwidget-url">http://</span>)</span>' +
    '</a>',

Definition of editables is as follows:

editables: {
    text: {
        selector: '.linkwidget-text',
        allowedContent: 'strong em'
    },
    url: {
        selector: '.linkwidget-url',
        allowedContent: ''
    }
},

Initialization of editables fail in widget.initEditable() because 'span' is not defined in CKEDITOR.dtd.$editable, i.e., following condition fails for 'span' elements:

editable.is( CKEDITOR.dtd.$editable )

[Piotrek Koszuliński]

DUP of #10974.