The pattern comes from a schema file. For example line some_option[/\d+/]["key"] contains
pattern [/\d+/]["key"]. It can contain regular expressions to match multiple / dynamic keys.
Examples:
For $value = [0 => [key => value], 1 => [key => value]]
And $pathInStructure = [0]["key"]
Returns [[0, key]]
For the same $value nad $pathInStructure = [/\d+/]["key"]
Returns [[0, key], [1, key]]