Semantics of readOnlySnapshot()

Question

I am trying to understand the following statement from the official doc:

https://www.scala-lang.org/api/current/scala/collection/concurrent/TrieMap.html

/** Returns a read-only snapshot of this TrieMap. This operation is lock-free 
 *  and linearizable.
 *
 *  The snapshot is lazily updated - the first time some branch of this TrieMap are
 *  accessed, it is rewritten. The work of creating the snapshot is thus
 *  distributed across subsequent updates and accesses on this TrieMap by all
 *  threads. Note that the snapshot itself is never rewritten unlike when calling
 *  the snapshot method, but the obtained snapshot cannot be modified.
 */
def readOnlySnapshot(): collection.Map[K, V]

1. The snapshot is lazily updated - the first time some branch of this TrieMap are accessed, it is rewritten. Does this mean that I only get the snapshot at the time I start to access/read some of the keys? Rather than the snapshot at the time I call readOnlySnapshot()?
2. Note that the snapshot itself is never rewritten unlike when calling the snapshot method, but the obtained snapshot cannot be modified. What would be a good example to demonstrate this?

Some code examples might help here.