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Nodes are navigated by name, using a navigation stack.
Every movement down adds a node to the stack, and every movement up removes one node from the stack.
Additionally, lateral movement is available, for nodes whose contents span mulitple pages.
All VM executions require an entry point.
If not explicitly set in the code, the node name root is used.
Attempting to navigate up from the entry point node will fail and terminate execution.
Lateral navigation is only available for node output spanning multiple pages. See Multi-page rendering for details.
Lateral navigation will fail and terminate execution when:
Regular node names must start with an alphabetical character. The rest of the string may contain alphanumeric characters and underscore.
A selection of special node names are available for relative navigation. They are single-character tokens, listed below with their respective ASCII codes.
. (0x2E)Repeat the same node.
_ (0x5F)Go to the previous node in the stack.
> (0x3E)Go to the next page of a multi-page node. Will fail if used in a single-page context and/or resulting page index is out of bounds.
< (0x3C)Go to the next page of a multi-page node. Will fail if used on the first (or single) page.
^ (0x5E)Go to the topmost node. Will execute each intermediate node in the stack.
Uncaught exceptions in the code flow that should not halt execution are routed to a builtin node named _catch.
Consider the following navigation example, illustrating the state of the stack for each step after execution.
| instruction | stack | page index |
|---|---|---|
MOVE foo | foo | 0 |
MOVE bar | foo/bar | 0 |
MOVE baz | foo/bar/baz | 0 |
MOVE > | foo/bar/baz | 1 |
MOVE > | foo/bar/baz | 2 |
MOVE < | foo/bar/baz | 1 |
MOVE . | foo/bar/baz | 1 |
MOVE _ | foo/bar | 0 |
MOVE baz | foo/bar/baz | 0 |
MOVE ^ | foo | 0 |
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