What does this do?

Every theme you apply has a name and a set of colour and style choices. This feature lets you copy a special web address that carries your exact theme inside it. When someone else opens that link, the page automatically shows in your theme — without them having to find and apply it themselves.

Which version do I use?

Start of address (? …)

Use this when you are sharing a plain web address, for example https://hyperpolyglot.io. The theme information is added right after the page address, starting with a ?.

Add to existing address (& …)

Use this when the address you are sharing already has a ? somewhere in it. The theme information is added after whatever is already there, using an & to separate it. If you are not sure, look at the address in your browser — if you see a ? after the page name, use this version.

Will it work on any website?

No — only on websites that display the WCP Compliant badge. The badge means the website understands this kind of theme address and knows what to do with it. You will usually find the badge in the page footer.

On other websites the link will still open the page normally — it just will not change the colours.