--- a/src/core/ngx_file.c
+++ b/src/core/ngx_file.c
@@ -563,6 +563,24 @@ failed:
 }
 
 
+/*
+ * ctx->init_handler() - see ctx->alloc
+ * ctx->file_handler() - file handler
+ * ctx->pre_tree_handler() - handler is called before entering directory
+ * ctx->post_tree_handler() - handler is called after leaving directory
+ * ctx->spec_handler() - special (socket, FIFO, etc.) file handler
+ *
+ * ctx->data - some data structure, it may be the same on all levels, or
+ *     reallocated if ctx->alloc is nonzero
+ *
+ * ctx->alloc - a size of data structure that is allocated at every level
+ *     and is initilialized by ctx->init_handler()
+ *
+ * ctx->log - a log
+ *
+ * on fatal (memory) error handler must return NGX_ABORT to stop walking tree
+ */
+
 ngx_int_t
 ngx_walk_tree(ngx_tree_ctx_t *ctx, ngx_str_t *tree)
 {