{{/* abono-subscribe-button — a POST form that starts Checkout. A POST
     because the handler mints a Stripe session; csrf.Protect checks the
     origin, so there is no token to carry.

     The form sends plan, interval (when there is one) and code (when Code
     is set), to Action.

     Keys:
       Action    string, required — where the form posts
       Plan      string, required — the plan to buy
       Interval  string, optional — "month" or "year"; empty sends none,
                 and Checkout takes the plan's only sold price
       Label     string, optional — the button's words; "abono.button.subscribe" by default
       Code      bool, optional — a promotion code field above the button
       L         *ui.Localizer */}}
{{define "abono-subscribe-button"}}{{$L := localizer $}}{{$id := printf "abono-code-%s-%s" .Plan (or (opt . "Interval") "any")}}<form rst-form-actions method="post" action="{{.Action}}"><input type="hidden" name="plan" value="{{.Plan}}">{{with opt . "Interval"}}<input type="hidden" name="interval" value="{{.}}">{{end}}{{if opt . "Code"}}<div rst-field><label rst-field-label for="{{$id}}">{{T $L "abono.plan.code_label"}}</label><input rst-input id="{{$id}}" name="code" type="text" autocomplete="off" autocapitalize="characters" spellcheck="false" aria-describedby="{{$id}}-hint"><small rst-field-hint id="{{$id}}-hint">{{T $L "abono.plan.code_hint"}}</small></div>{{end}}<button type="submit" rst-btn="primary">{{with opt . "Label"}}{{.}}{{else}}{{T $L "abono.button.subscribe"}}{{end}}</button></form>{{end}}