diff --git a/texindex/unicode.awk b/texindex/unicode.awk
new file mode 100644
index 0000000..c03baaa
--- /dev/null
+++ b/texindex/unicode.awk
@@ -0,0 +1,20 @@
+BEGIN {
+	printf("0x10FFFF is %d\n", 0x10FFFF)
+	printf("0xFFFD is %d\n", 0xFFFD)
+	printf("0xFFFD is '%c'\n", 0xFFFD)
+	invalid = sprintf("%c\n", 0xFFFD)
+
+	count = 0
+	for (i = 0; i <= 0x10FFFF; i++) {
+		char = sprintf("%c", i)
+		if (isvalid(char))
+			count++
+	}
+
+	printf("%d valid characters between 1 and %d\n", count, 0x10FFFF)
+}
+
+function isvalid(c)
+{
+	return c ~ /[[:alpha:][:blank:][:cntrl:][:digit:][:graph:][:lower:][:print:][:punct:][:space:][:upper:]]/
+}