What are these enclosed box characters?

Question

When you enclose something it's in this little box. Sometimes there are these symbols making up the box. Arrows, broken lines, tildes, epsilons. What do they mean

Answer 1

If you turn boxing on with -style=max (or use ]Display) you will see these characters in the borders of the boxes. E.g. with ]box on -style=max:

      1 3⍴'123' ⍬ ('1'2)
┌→────────────────┐
↓ ┌→──┐ ┌⊖┐ ┌→──┐ │
│ │123│ │0│ │1 2│ │
│ └───┘ └~┘ └+──┘ │
└∊────────────────┘

The →s mean that there is a trailing axis. The ↓ means that there is an additional axis. So the outer shape is a matrix. Its ∊ means that it is nested.

The smooth bottom border of 123 means it is a character (not numeric) vector (indicated by the single axis; →).

The ~ means numeric array, and it has a single zero-length axis indicated by ⊖. (Also the prototype is a single 0).

The + means mixed type (here: character and numeric). Note that this vector is not nested.

In summary, the symbols are ∊ for nested, ~ for numeric, ─ for character, # for namespace, ∇ for object representation, and + for Mixed. The full documentation can be obtained with ]???box. Try it online!