This simple bot implements a context extending and illustrates usage of Custom Entities.
How to use
You have to create cities entity and upload cities.csv file in your bot's preferences to generate Custom Entity of all cities in the world. So your bot could recognize city by name.
Then you can ask your bot about the weather in different cities and dates. Just note that this bot doesn't actually fetch weather data. It just responds with hardcoded answers.
Just look into the bot's JSON response. You will see a date and city details, like latitude and longitude and etc.