I'm building a skill in the UK that requires asking the user for a more precise location that their home city. The skills will tell you if any cycle hire bikes (see https://tfl.gov.uk/modes/cycling/santander-cycles) are available near your location.
In the UK, it's easy to get a relatively precise location by asking for a postcode, which is a combination of letters & numbers (example: SW15 5PU, see also https://en.wikipedia.org/wiki/Postcodes_in_the_United_Kingdom#Validation).
What would be a suitable slot type to use to recognise such postcodes? I could use a custom slot but there are more than 1 million postcodes, so what sort of examples should I put?