Index: wp-includes/query.php
===================================================================
--- wp-includes/query.php	(revision 12726)
+++ wp-includes/query.php	(working copy)
@@ -193,6 +193,42 @@
 }
 
 /**
+ * Determine whether the current query is for the given taxonomy or a term
+ * in that taxonomy.
+ * 
+ * @param string $taxonomy The taxonomy name. Required.
+ * @param int|array|string $term The term's ID, array of term IDs, or term slug.
+ * @return bool If the given taxonomy and term or terms  
+ * query, true; otherwise, false.
+ */
+function is_tax_term($taxonomy, $term = null) {
+	global $wp_query, $wp_taxonomies;
+
+	if ( 
+		( $wp_query->is_tax || $wp_query->is_category || $wp_query->is_tag ) &&
+		in_array($taxonomy, array_keys($wp_taxonomies)) 
+	) {
+		$queried_object = $wp_query->get_queried_object();
+		if ( isset($queried_object->taxonomy) && isset($queried_object->term_id) ) {
+			$term_array = (array) $term;
+			if ( 
+				$taxonomy == $queried_object->taxonomy &&
+				(
+					empty( $term ) ||
+					count(array_intersect(
+						array($queried_object->term_id, $queried_object->name, $queried_object->slug), 
+						$term_array
+					))
+				)
+			) {
+				return true;
+			}
+		}
+	}
+	return false;
+}
+
+/**
  * Whether the current page query has the given tag slug or contains tag.
  *
  * @since 2.3.0