Error messages related to dotted keys looks weird. like:
1 | a.b.c = 42
| ~~ in this table
The underlined token is not a table. This should be like the following.
1 | a.b.c = 42
| ~~~ in this table
To implement this, the region information is needed when the keys are
read. This commit add this functionality, though currently the region
information is not used yet.