Layer-s are responsible for collecting and ordering Clip-s.
A layer within a timeline will have an associated priority, corresponding to their index within the timeline. A layer with the
index/priority 0 will have the highest priority and the layer with the largest index will have the lowest priority (the order of
priorities, in this sense, is the _reverse_ of the numerical ordering of the indices).
move_layer should be used if you wish to change how layers are prioritised in a
timeline.
Layers with higher priorities will have their content priorities over content from lower priority layers, similar to how layers are used
in image editing. For example, if two separate layers both display video content, then the layer with the higher priority will have its
images shown first. The other layer will only have its image shown if the higher priority layer has no content at the given playtime, or
is transparent in some way. Audio content in separate layers will simply play in addition.
Retrieves the duration of the layer, which is the difference between
the start of the layer (always time 0) and the end (which will be the end time of the final clip).