The sw HTML image export already uses HtmlWriter, so need to extend this to support XHTML alternate text, writing the character data directly is not an option. Change-Id: Iac3f2b9a3828175a5f1d0fb14ab505f8de389e52 Reviewed-on: https://gerrit.libreoffice.org/50965 Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk> Tested-by: Jenkins <ci@libreoffice.org>