@function _oHeaderServicesLogo($logo) {
	// Error if the global $system-code variable is not set.
	// This is required for image service requests.
	@if(global-variable-exists('system-code') == false or type-of($system-code) != 'string') {
		@error 'A global "$system-code" Sass variable must be set to a valid [Bizops system code](https://biz-ops.in.ft.com/list/Systems).';
	}
	
	@if str-index($logo, 'https://') == 1 or str-index($logo, 'http://') == 1 or str-index($logo, 'data:') == 1 or str-index($logo, './') == 1 or str-index($logo, '../') == 1 or str-index($logo, '/') == 1 {
		@return $logo;
	} @else {
		@return 'https://www.ft.com/__origami/service/image/v2/images/raw/#{$logo}?source=#{$system-code}&format=svg&width=55';
	}
}