[question?] counterintuitive class method behaviour

When I write a query like this:
```codeql
class Meow extends Struct {
Field f;
Meow() {
f.getDeclaringType() = this
}
Field getField() { result = f }
}

from Meow m
select m, m.getField(), m.getField()
```
My mental model of this is: "`Meow` is essentially a (struct, struct's field) tuple. `from Meow m` will select all of those tuples. For each of those , `select m, m.getField(), m.getField()` will print their contents."

But that is actually not what happens, because you get results like this:
```
| m | col1 | col2 |
+-----------------------------------+-----------------------------------------------------+-----------------------------------------------------+
// [snip]
| port_io_ops | f_inb | f_outb |
// [snip]
```
Which means that the first `m.getField()` and the second `m.getField()` are operating on different `Meow` objects.

I've been debugging a bug in my query for hours now only to realize that this is what happens. Is this really intended? I read through a non-trivial amount of documentation and did not realize this, I feel like my whole mental model of how codeql works is shattering :S

(If it is really intended, could the documentation be updated to point this out more clearly?)

Start with the CodeQL query and output shown in the issue, then read the documentation covering class methods and predicate evaluation. Confirm the intended behavior and identify the relevant documentation section; done means the behavior is explained clearly enough to address the reported mental-model gap.

索引モデルが issue の本文から書いたものです。