Insert character at specific point but preserving tags?

Question

Update #2

Okay, more testing ensues. It looks like the code works fine when I use a faux spacer, but the regex eventually fails. Specifically, the following scenari

Answer 1

Here is a solution that supports all the features from your requirements:

HTML:

    First Line
    
    
    Second Line
    
    Third Line
    
    Forth Line

CSS:

.space {
    display: inline-block;
    width: 100%;
}
.highlighting {
    background-color: green;
}

JavaScript:

var text,
    output,
    unwrapContents,
    mergeElements,
    clearSelection,
    clearHighlighting,
    mergeHighlighting,
    handleCopy;

unwrapContents = function unwrapContents(element) {
    while(element.firstChild !== null) {
        element.parentNode.insertBefore(element.firstChild, element);
    }
    element.parentNode.removeChild(element);
};

mergeElements = function mergeElements(startElement, endElement) {
    var currentElement;
    endElement = endElement.nextSibling;
    while((currentElement = startElement.nextSibling) !== endElement) {
        startElement.appendChild(currentElement);
    }
};

clearSelection = function clearSelection() {
    if (document.selection) {
        document.selection.empty();
    } else if (window.getSelection) {
        window.getSelection().removeAllRanges();
    }
};

clearHighlighting = function clearHighlighting(target, exception) {
    $('.highlighting', target).each(function(index, highlighting) {
        if(highlighting !== exception) {
            unwrapContents(highlighting);
        }
    });
    target.normalize();
};

mergeHighlighting = function mergeHighlighting() {
    var i, j;
    // Remove internal highlights
    $('.highlighting', text).filter(function() {
        return this.parentNode.className === 'highlighting';
    }).each(function(index, highlighting) {
        unwrapContents(highlighting);
    });
    text.normalize();
    // Merge adjacent highlights
    first:
    for(i=0; i

Here is a working example http://jsbin.com/efohit/3/edit