Page URI looks like this: http://localhost/index?text=abc%20def%20ert&base=base1 Template xml looks like this: <a> <n:attr name="href"><n:slot name="href" /></n:attr> <n:slot name="base" />(<n:slot name="count" />) </a> Render code looks like this: def render_href(self, ctx, data): u = url.URL.fromContext(ctx) u = u.replace("base", data[0]) ctx.fillSlots("href", u) ctx.fillSlots("base", data[0]) ctx.fillSlots("count", data[1]) return ctx.tag Problem: In this example, href of A-tag is not url-encoded. So, i have a link, that looks like this: <a href="http://localhost/index?text=abc def ert&base=base2"> (there are spaces in href) To make valid link, i need to do urllib.quote by myself: from urllib import quote ctx.fillSlots("href", quote(str(u),':&/=?')) Why URL flattener avoid urllib.quote? P.S. And may be using urllib.unquote_plus() is more correct in url.URL than urllib.unquote()? (IE encoded form data spaces into '+' chars, not into '%20') P.P.S. nevow 0.4.1