This tool allows labeling of polyline contours. It works on polylines and on XRefs containing polyline contours.
Update version: now include Spline entities, and optional user-Layer.

Attach your topographic polyline-contours and label them right inside the host DWG. Do you really need to triangulate your static topographic base contours as background? Sometimes you can't, especially since most topographic backgrounds are huge. This is useful for non Autodesk® Civil 3D® DWG's without the need to convert the polylines into a Civil 3D TIN Surface.

The tool captures the polyline elevations and places them as contour labels. The Labels are masked and placed in the same layer as source polyline but suffixed with "-LABL".

Tweak the Settings to "Block Mode" and allow the labels to be placed in a block for easier manipulation. Settings also allow for skipping minor contours using their layers, provided that minor and major contours are in different layers.