page/page.go
func (p PrintToPDFParams) WithHeaderTemplate(headerTemplate string) *PrintToPDFParams {
	p.HeaderTemplate = headerTemplate
	return &p
}
func (p PrintToPDFParams) WithHeaderTemplate(headerTemplate string) *PrintToPDFParams {
	p.HeaderTemplate = headerTemplate
	return &p
}
// WithHeaderTemplate HTML template for the print header. Should be valid
// HTML markup with following classes used to inject printing values into them:
// - date: formatted print date - title: document title - url: document location
// - pageNumber: current page number - totalPages: total pages in the document
// For example, <span class=title></span> would generate span containing the
// title.