Thank you, great to see osgEarth still being in active development. It provides a great service to us.
Is there more documentation regarding the features specified in the Release Notes though? E.g. is there an example for "TerrainConstraintLayer"? And mentioning "Improved task cancelation support throughout". What exactly is a task? A tile fetch via the DatabasePager? And from the 3.0 Release Notes: What are CompositeLayers and what service do they provide?
A TerrainConstraintLayer points to feature data that can "cut into" the terrain, to form a rigdeline, coastline, or a cut-out for a custom inset model. See "constraints.earth" for examples.
Sometimes a background task (like loading tiles) begins, but then is no longer relevant for some reason (camera moved away, user quits the app) and the task needs to be cancelled. The support for that is better now in various ways.
CompositeLayer lets you group multiple like layers together and treat them as a single layer. See "composite_image.earth" for an example.