JS Snippet taken from Sitecore's Content Editor.js that supports the toggle of field sections

ContentEditor_ToggleSection_Snippet.js

scContentEditor.prototype.toggleSection = function (id, sectionName) {
    var el = document.getElementById(id);
    if (el == null) {
        return;
    }
 
    var nextSibling = el.nextSibling;
    var visible = nextSibling.style.display == "none";
 
    el.className = visible ? "scEditorSectionCaptionExpanded" : "scEditorSectionCaptionCollapsed";
    jQuery(nextSibling).slideToggle(100);
 
    var scSections = document.getElementById("scSections");
    var value = scSections.value;
 
    var p = value.toQueryParams();
    p[sectionName] = visible ? "0" : "1";
    scSections.value = Object.toQueryString(p);
 
    var glyph = document.getElementById(id + "_Glyph");
    if (glyph != null) {
        var replace = (visible ? "/accordion_down" : "/accordion_up");
        var replaceWith = (visible ? "/accordion_up" : "/accordion_down");
 
        scForm.browser.setOuterHtml(glyph, scForm.browser.getOuterHtml(glyph).replace(replace, replaceWith));
    }
 
    if (this.onToggleSection) {
        for (var k = 0; k < this.onToggleSection.length; k++) {
            this.onToggleSection[k](id, sectionName);
        }
    }
}
//This function is taken from <Sitecore Web Root>\sitecore\shell\Applications\Content Manager\Content Editor.js. 
//It is a single snippet showing how field sections are collapsed and expanded.