+ */
+
+ // If given strings with astral codepoints or combining
+ // characters, split them into arrays of "glyphs" first,
+ // do the edit on the list of "glyphs", and rejoin them.
+ //
+ // This split is not perfect for all languages, but at least
+ // it won't create invalid surrogate pairs or orphaned
+ // combining characters.
+ if (source.match && (source.match(MULTI) || target.match(MULTI))) {
+ var sourceGlyphs = source.match(GLYPH) || [];
+ var targetGlyphs = target.match(GLYPH) || [];
+ return diffLerp(sourceGlyphs, targetGlyphs, amount).join("");
+ }
+
+ // The edit path works from the string end, forwards, because
+ // that's how Levenshtein edits work. To match LTR reading
+ // direction (and the behavior of fastLerp), swap the strings
+ // and invert the parameter when editing.
+ var edits = diff(target, source, 2, 2, 3);
+ var partial = edits.slice(0, Math.round((1 - amount) * edits.length));
+ return patch(partial, target);
+ }
+
+ var NUMBERS = /(-?\d+(?:\.\d+)?)/g;
+
+ function areNumericTwins(source, target) {
+ /** Check if a and b differ only in numerals */
+ return source.replace(NUMBERS, "0") === target.replace(NUMBERS, "0");
+ }
+
+ function nlerp(source, target, amount) {
+ return source + (target - source) * amount;
+ }
+
+ function numericLerp(source, target, amount) {
+ /** Interpolate numerically between strings containing numbers
+
+ Numbers may have a leading "-" and a single "." to mark
+ the decimal point, but something must be after the ".".
+ No other floating point syntax (e.g. 1e6) is supported.
+ If both of the numbers in a pair are integers, the result
+ is clamped to an integer.
+
+ For example, numericLerp("0.0", "100", 0.123) === "12.3"
+ because the "." in "0.0" is interpreted as a decimal
+ point. But numericLerp("0.", "100.", 0.123) === "12."
+ because the strings are interpreted as integers followed
+ by a full stop.
+
+ Calling this functions on strings that differ in more than
+ numerals gives undefined results.
+ */
+
+ // TODO: Try to preserve precision of the original numbers.
+ var sourceParts = source.split(NUMBERS);
+ var targetParts = target.split(NUMBERS);
+ var destParts = targetParts;
+ for (var i = 1; i < sourceParts.length; i += 2) {
+ var sourcePart = sourceParts[i];
+ var targetPart = targetParts[i];
+ var part = nlerp(+sourcePart, +targetPart, amount);
+ var sourcePoint = sourcePart.indexOf(".");
+ var targetPoint = targetPart.indexOf(".");
+ if (sourcePoint === -1 && targetPoint === -1)
+ part = Math.round(part);
+ targetParts[i] = part.toString();
+ }
+ return targetParts.join("");