source: node_modules/prismjs/plugins/keep-markup/prism-keep-markup.js

(function () {

        if (typeof Prism === 'undefined' || typeof document === 'undefined' || !document.createRange) {
                return;
        }

        Prism.plugins.KeepMarkup = true;

        Prism.hooks.add('before-highlight', function (env) {
                if (!env.element.children.length) {
                        return;
                }

                if (!Prism.util.isActive(env.element, 'keep-markup', true)) {
                        return;
                }

                var dropTokens = Prism.util.isActive(env.element, 'drop-tokens', false);
                /**
                 * Returns whether the given element should be kept.
                 *
                 * @param {HTMLElement} element
                 * @returns {boolean}
                 */
                function shouldKeep(element) {
                        if (dropTokens && element.nodeName.toLowerCase() === 'span' && element.classList.contains('token')) {
                                return false;
                        }
                        return true;
                }

                var pos = 0;
                var data = [];
                function processElement(element) {
                        if (!shouldKeep(element)) {
                                // don't keep this element and just process its children
                                processChildren(element);
                                return;
                        }

                        var o = {
                                // Store original element so we can restore it after highlighting
                                element: element,
                                posOpen: pos
                        };
                        data.push(o);

                        processChildren(element);

                        o.posClose = pos;
                }
                function processChildren(element) {
                        for (var i = 0, l = element.childNodes.length; i < l; i++) {
                                var child = element.childNodes[i];
                                if (child.nodeType === 1) { // element
                                        processElement(child);
                                } else if (child.nodeType === 3) { // text
                                        pos += child.data.length;
                                }
                        }
                }
                processChildren(env.element);

                if (data.length) {
                        // data is an array of all existing tags
                        env.keepMarkup = data;
                }
        });

        Prism.hooks.add('after-highlight', function (env) {
                if (env.keepMarkup && env.keepMarkup.length) {

                        var walk = function (elt, nodeState) {
                                for (var i = 0, l = elt.childNodes.length; i < l; i++) {

                                        var child = elt.childNodes[i];

                                        if (child.nodeType === 1) { // element
                                                if (!walk(child, nodeState)) {
                                                        return false;
                                                }

                                        } else if (child.nodeType === 3) { // text
                                                if (!nodeState.nodeStart && nodeState.pos + child.data.length > nodeState.node.posOpen) {
                                                        // We found the start position
                                                        nodeState.nodeStart = child;
                                                        nodeState.nodeStartPos = nodeState.node.posOpen - nodeState.pos;
                                                }
                                                if (nodeState.nodeStart && nodeState.pos + child.data.length >= nodeState.node.posClose) {
                                                        // We found the end position
                                                        nodeState.nodeEnd = child;
                                                        nodeState.nodeEndPos = nodeState.node.posClose - nodeState.pos;
                                                }

                                                nodeState.pos += child.data.length;
                                        }

                                        if (nodeState.nodeStart && nodeState.nodeEnd) {
                                                // Select the range and wrap it with the element
                                                var range = document.createRange();
                                                range.setStart(nodeState.nodeStart, nodeState.nodeStartPos);
                                                range.setEnd(nodeState.nodeEnd, nodeState.nodeEndPos);
                                                nodeState.node.element.innerHTML = '';
                                                nodeState.node.element.appendChild(range.extractContents());
                                                range.insertNode(nodeState.node.element);
                                                range.detach();

                                                // Process is over
                                                return false;
                                        }
                                }
                                return true;
                        };

                        // For each tag, we walk the DOM to reinsert it
                        env.keepMarkup.forEach(function (node) {
                                walk(env.element, {
                                        node: node,
                                        pos: 0
                                });
                        });
                        // Store new highlightedCode for later hooks calls
                        env.highlightedCode = env.element.innerHTML;
                }
        });
}());