path FEATURE variables instead of values

Supported now for node-instance-identifier.
diff --git a/src/xpath.h b/src/xpath.h
index c34a0f3..803de7d 100644
--- a/src/xpath.h
+++ b/src/xpath.h
@@ -497,15 +497,17 @@
         enum lyxp_token want_tok1, enum lyxp_token want_tok2);
 
 /**
- * @brief Find variable named @name in @p vars.
+ * @brief Find variable named @p name in @p vars.
  *
+ * @param[in] ctx Context for logging, not logged if NULL.
  * @param[in] vars [Sized array](@ref sizedarrays) of XPath variables.
  * @param[in] name Name of the variable being searched.
  * @param[in] name_len Name length can be set to 0 if @p name is terminated by null byte.
  * @param[out] var Variable that was found. The parameter is optional.
  * @return LY_SUCCESS if the variable was found, otherwise LY_ENOTFOUND.
  */
-LY_ERR lyxp_vars_find(struct lyxp_var *vars, const char *name, size_t name_len, struct lyxp_var **var);
+LY_ERR lyxp_vars_find(const struct ly_ctx *ctx, const struct lyxp_var *vars, const char *name, size_t name_len,
+        struct lyxp_var **var);
 
 /**
  * @brief Frees a parsed XPath expression. @p expr should not be used afterwards.