// matroska-demux.h
...

  /* Cached upstream length (default G_MAXUINT64) */
  guint64              cached_length;

  GstTagList              *tag_list;
} GstMatroskaDemux;
...
// matroska-demux.c
...
static GstFlowReturn
gst_matroska_demux_chain (GstPad * pad, GstObject * parent, GstBuffer * buffer)
{
  GstMatroskaDemux *demux = GST_MATROSKA_DEMUX (parent);
  guint available;
  GstFlowReturn ret = GST_FLOW_OK;
  guint needed = 0;
  guint32 id;
  guint64 length;

  if (demux->tag_list) {
    gst_matroska_read_common_found_global_tag (&demux->common, GST_ELEMENT_CAST (demux), demux->tag_list);
    gst_matroska_demux_send_tags (demux);
    demux->tag_list = NULL;
  }
...
static gboolean
gst_matroska_demux_handle_sink_event (GstPad * pad, GstObject * parent,
    GstEvent * event)
{
  gboolean res = TRUE;
  GstMatroskaDemux *demux = GST_MATROSKA_DEMUX (parent);

  GST_DEBUG_OBJECT (demux,
      "have event type %s: %p on sink pad", GST_EVENT_TYPE_NAME (event), event);

  switch (GST_EVENT_TYPE (event)) {
    case GST_EVENT_TAG:
    {
      gst_event_parse_tag (event, &demux->tag_list);
      break;
    }
...