diff --git a/tailbone/static/js/numeric.js b/tailbone/static/js/numeric.js
new file mode 100644
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+++ b/tailbone/static/js/numeric.js
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+
+
+/*
+ * Determine if a keypress would modify the value of a textbox.
+ *
+ * Note that this implies that the keypress is also *valid* in the context of a
+ * numeric textbox.
+ *
+ * Returns `true` if the keypress is valid and would modify the textbox value,
+ * or `false` otherwise.
+ */
+function key_modifies(event) {
+
+    if (event.which >= 48 && event.which <= 57) {       // Numeric (QWERTY)
+        if (! event.shiftKey) {  // shift key means punctuation instead of numeric
+            return true;
+        }
+
+    } else if (event.which >= 96 && event.which <= 105) { // Numeric (10-Key)
+        return true;
+
+    } else if (event.which == 8) {                      // Backspace
+        return true;
+
+    } else if (event.which == 46) {                     // Delete
+        return true;
+    }
+
+    return false;
+}
+
+
+/*
+ * Determine if a keypress is allowed in the context of a textbox.
+ *
+ * The purpose of this function is to let certain "special" keys (e.g. function
+ * and navigational keys) to pass through, so they may be processed as they
+ * would for a normal textbox.
+ *
+ * Note that this function does *not* check for keys which would actually
+ * modify the value of the textbox.  It is assumed that the caller will have
+ * already used `key_modifies()` for that.
+ *
+ * Returns `true` if the keypress is allowed, or `false` otherwise.
+ */
+function key_allowed(event) {
+
+    // Allow anything with modifiers (except Shift).
+    if (event.altKey || event.ctrlKey || event.metaKey) {
+        return true;
+    }
+
+    // Allow function keys.
+    if (event.which >= 112 && event.which <= 123) {
+        return true;
+    }
+
+    // Allow Home/End/arrow keys.
+    if (event.which >= 35 && event.which <= 40) {
+        return true;
+    }
+
+    // Allow Tab key.
+    if (event.which == 9) {
+        return true;
+    }
+
+    return false;
+}