diff --git a/common/opentype.c b/common/opentype.c
new file mode 100644
index 00000000..7ed1062c
--- /dev/null
+++ b/common/opentype.c
@@ -0,0 +1,147 @@
+// 25 february 2018
+#include "uipriv.h"
+#include "attrstr.h"
+
+struct feature {
+	char a;
+	char b;
+	char c;
+	char d;
+	uint32_t value;
+};
+
+struct uiOpenTypeFeatures {
+	struct feature *data;
+	size_t len;
+	size_t cap;
+};
+
+#define bytecount(n) ((n) * sizeof (struct feature))
+
+uiOpenTypeFeatures *uiNewOpenTypeFeatures(void)
+{
+	uiOpenTypeFeatures *otf;
+
+	otf = uiprivNew(uiOpenTypeFeatures);
+	otf->cap = 16;
+	otf->data = (struct feature *) uiprivAlloc(bytecount(otf->cap), "struct feature[]");
+	otf->len = 0;
+	return otf;
+}
+
+void uiFreeOpenTypeFeatures(uiOpenTypeFeatures *otf)
+{
+	uiprivFree(otf->data);
+	uiprivFree(otf);
+}
+
+// uiOpenTypeFeaturesClone() makes a copy of otf and returns it.
+// Changing one will not affect the other.
+_UI_EXTERN uiOpenTypeFeatures *uiOpenTypeFeaturesClone(const uiOpenTypeFeatures *otf)
+{
+	uiOpenTypeFeatures *ret;
+
+	ret = uiprivNew(uiOpenTypeFeatures);
+	ret->len = otf->len;
+	ret->cap = otf->cap;
+	ret->data = (struct feature *) uiprivAlloc(bytecount(ret->cap), "struct feature[]");
+	memset(ret->data, 0, bytecount(ret->cap));
+	memmove(ret->data, otf->data, bytecount(ret->len));
+	return ret;
+}
+
+#define intdiff(a, b) (((int) (a)) - ((int) (b)))
+
+static int featurecmp(const void *a, const void *b)
+{
+	const struct feature *f = (const struct feature *) a;
+	const struct feature *g = (const struct feature *) b;
+
+	if (f->a != g->a)
+		return intdiff(f->a, g->a);
+	if (f->b != g->b)
+		return intdiff(f->b, g->b);
+	if (f->c != g->c)
+		return intdiff(f->c, g->c);
+	return intdiff(f->d, g->d);
+}
+
+void uiOpenTypeFeaturesAdd(uiOpenTypeFeatures *otf, char a, char b, char c, char d, uint32_t value)
+{
+	struct feature *f;
+
+	// replace existing value if any
+	f = (struct feature *) bsearch(otf->data, otf->len, sizeof (struct feature), featurecmp);
+	if (f != NULL) {
+		f->value = value;
+		return;
+	}
+
+	// if we got here, the tag is new
+	if (otf->len == otf->cap) {
+		otf->cap *= 2;
+		otf->data = (struct feature *) uiprivRealloc(otf->data, bytecount(otf->cap), "struct feature[]");
+	}
+	f = otf->data + otf->len;
+	f->a = a;
+	f->b = b;
+	f->c = c;
+	f->d = d;
+	f->value = value;
+	// TODO qsort here is overkill
+	otf->len++;
+	qsort(otf->data, otf->len, sizeof (struct feature), featurecmp);
+}
+
+_UI_EXTERN void uiOpenTypeFeaturesRemove(uiOpenTypeFeatures *otf, char a, char b, char c, char d)
+{
+	struct feature *f;
+	ptrdiff_t index;
+	size_t count;
+
+	f = (struct feature *) bsearch(otf->data, otf->len, sizeof (struct feature), featurecmp);
+	if (f == NULL)
+		return;
+
+	index = f - otf->data;
+	count = otf->len - index - 1;
+	memmove(f + 1, f, bytecount(count));
+	otf->len--;
+}
+
+int uiOpenTypeFeaturesGet(const uiOpenTypeFeatures *otf, char a, char b, char c, char d, uint32_t *value)
+{
+	const struct feature *f;
+
+	f = (const struct feature *) bsearch(otf->data, otf->len, sizeof (struct feature), featurecmp);
+	if (f == NULL)
+		return 0;
+	*value = f->value;
+	return 1;
+}
+
+void uiOpenTypeFeaturesForEach(const uiOpenTypeFeatures *otf, uiOpenTypeFeaturesForEachFunc f, void *data)
+{
+	size_t n;
+	const struct feature *p;
+	uiForEach ret;
+
+	p = otf->data;
+	for (n = 0; n < otf->len; n++) {
+		ret = (*f)(cur->a, cur->b, cur->c, cur->d,
+			cur->value, data);
+		// TODO for all: require exact match?
+		if (ret == uiForEachStop)
+			return;
+		p++;
+	}
+}
+
+int uiprivOpenTypeFeaturesEqual(const uiOpenTypeFeatures *a, const uiOpenTypeFeatures *b)
+{
+	if (a == b)
+		return 1;
+	if (a->len != b->len)
+		return 0;
+	return memcmp(a->data, b->data, bytecount(a->len)) == 0;
+}