Example controller per https://github.com/revault/desktop.rebol.info/pull/1

addsite.reb

Rebol [
    Title: "Add a Site"
    Type: 'controller
    File: %app/controllers/addsite.r
]

route () to submit [  ; where submit is %app/views/addsite/submit.html.rsp
    get [] ; shows the form

    put [
        if verify [
            submission: get-params/body 'site [
                reject 400 "No New Site data"
            ]

            submission: validate submission [
                name: string! length is less-than 50
                info: opt string! length is less-than 240
                site: url!
            ][] ; doing nothing will show the form again

            attempt [load/header submission/site][
                reject 400 "Could not reach your site"
            ]
        ][
            sites-list: read index: wrt://site/rebsite.r  ; uses the internal wrt:// filesystem scheme
            write index append sites-list join newline remold [
                'folder submission/name submission/site 'icon 'site 'info submission/info
            ]

            redirect-to %/show?http://desktop.rebol.info/rebsites.r
        ]
    ]
]