function createGridLineElement(glOpts, defaults, type) {
		type = type || 'major';
		var tagName = 'c:'+ type + 'Gridlines';
		strXml =  '<'+ tagName + '>';
		strXml += ' <c:spPr>';
		strXml += '  <a:ln w="' + Math.round((glOpts.size || defaults.size) * ONEPT) +'" cap="flat">';
		strXml += '  <a:solidFill><a:srgbClr val="' + (glOpts.color || defaults.color) + '"/></a:solidFill>'; // should accept scheme colors as implemented in PR 135
		strXml += '   <a:prstDash val="' + (glOpts.style || defaults.style) + '"/><a:round/>';
		strXml += '  </a:ln>';
		strXml += ' </c:spPr>';
		strXml += '</'+ tagName + '>';
		return strXml;
	}
@param {Object} glOpts {size, color, style}
@param {Object} defaults {size, color, style}
@param {String} type "major"(default) | "minor"