copy-tex contrib module (#813)

* copy-tex contrib module

* Factor out replacement code

* Fix lint

* Support for more browsers, in particular Firefox

* Use for loop instead of Array.forEach
* Use replaceChild if replaceWith is unavailable
* Browserify to remove let etc.

* Fix HTML handling, in particular for Edge

* Convert DocumentFragment to HTML directly (via children' outerHTML)
* Set HTML content *before* text content; Edge takes the last only

* Handle .katex-html and .katex-mathml separately

* Implement option 2: CSS user-select: all

Also fix auto-render.js build location

* Revise documentation according to @kevinbarabash's comments

* Split copy-tex.js into it + katex2tex.js

This supports re-use of code in a custom copy handler.

* Document custom copy handler

* Add missing file

contrib/copy-tex/katex2tex.js

@@ -0,0 +1,52 @@
+// Set these to how you want inline and display math to be delimited.
+export const defaultCopyDelimiters = {
+    inline: ['$', '$'],    // alternative: ['\(', '\)']
+    display: ['$$', '$$'], // alternative: ['\[', '\]']
+};
+
+// Replace .katex elements with their TeX source (<annotation> element).
+// Modifies fragment in-place.  Useful for writing your own 'copy' handler,
+// as in copy-tex.js.
+export const katexReplaceWithTex = function(fragment,
+    copyDelimiters = defaultCopyDelimiters) {
+    // Remove .katex-html blocks that are preceded by .katex-mathml blocks
+    // (which will get replaced below).
+    const katexHtml = fragment.querySelectorAll('.katex-mathml + .katex-html');
+    for (let i = 0; i < katexHtml.length; i++) {
+        const element = katexHtml[i];
+        if (element.remove) {
+            element.remove(null);
+        } else {
+            element.parentNode.removeChild(element);
+        }
+    }
+    // Replace .katex-mathml elements with their annotation (TeX source)
+    // descendant, with inline delimiters.
+    const katexMathml = fragment.querySelectorAll('.katex-mathml');
+    for (let i = 0; i < katexMathml.length; i++) {
+        const element = katexMathml[i];
+        const texSource = element.querySelector('annotation');
+        if (texSource) {
+            if (element.replaceWith) {
+                element.replaceWith(texSource);
+            } else {
+                element.parentNode.replaceChild(texSource, element);
+            }
+            texSource.innerHTML = copyDelimiters.inline[0] +
+                texSource.innerHTML + copyDelimiters.inline[1];
+        }
+    }
+    // Switch display math to display delimiters.
+    const displays = fragment.querySelectorAll('.katex-display annotation');
+    for (let i = 0; i < displays.length; i++) {
+        const element = displays[i];
+        element.innerHTML = copyDelimiters.display[0] +
+            element.innerHTML.substr(copyDelimiters.inline[0].length,
+                element.innerHTML.length - copyDelimiters.inline[0].length
+                - copyDelimiters.inline[1].length)
+            + copyDelimiters.display[1];
+    }
+    return fragment;
+};
+
+module.exports = katexReplaceWithTex;