command macgap.localfile.read("path/to/file")

that allows to read files from filesystem as long as filename is whitelisted

One can use that to include user provided css or scripts. Example

webapp:
``` javascript
if (window.macgap.localfile) {
    var json = macgap.localfile.read("~/my_app_userstyle.css");
    if (json) {
        response = $.parseJSON(json);
        if (response && response.content) {
            css = response.content;
            var styleNode = document.createElement('style');
            styleNode.type = "text/css";
            var styleText = document.createTextNode(css);
            styleNode.appendChild(styleText);
            document.getElementsByTagName('head')[0].appendChild(styleNode);
        }
    }
}
```

and in public/localfiles.whitelist
```
~/my_app_userstyle.css
```