jQuery nextUntil include text nodes

You can create your own jquery plugin which does the same as nextUntil but includes text nodes:

$.fn.nextUntilWithTextNodes = function (until) {
    var matched = $.map(this, function (elem, i, until) {
        var matched = [];
        while ((elem = elem.nextSibling) && elem.nodeType !== 9) {
            if (elem.nodeType === 1 || elem.nodeType === 3) {
                if (until && jQuery(elem).is(until)) {
                    break;
                }
                matched.push(elem);
            }
        }
        return matched;
    }, until);

    return this.pushStack(matched);
};

So you can call this nextUntilWithTextNodes instead of nextUntil and you are good to go.

Only the jQuery .contents() method returns all nodes (including text nodes, normally ignored).

So maybe something like this?:

http://jsfiddle.net/ykv3gf5L/2/

$('.content').each(function () {
    var open = false;
    var result = $();
    $(this).contents().each(function () {
        var $this = $(this);
        if ($this.text() == "spoiler") {
            if (open) {
                result.wrapAll('<div style="border:solid 1px black;"></div>');
                open = false;
            } else {
                result = $();
                open = true;
            }
        } else {
            result = result.add($this)
        }
    });
    if (open) {
        result.wrapAll('<div style="border:solid 1px black;"></div>');
    }
});

It just iterate all nodes and based on a flag starts a new collection, or wraps the nodes found.

The final if (open) allows for an unclosed spolier block within a content classed div.

Notes:

• $() is an empty jQuery collection (like an empty array but for jQuery objects)
• I suggest you use a style for your spoilers and use a class e.g. result.wrapAll('<div class="spoiler"></div>');

e.g. http://jsfiddle.net/ykv3gf5L/3/