document localization template interpolation, like ${0}

[jimmont]

please update or expand the localization docs to help those (manually) creating templates for runtime localization that show how to use interpolation and what does and doesn't work, for example a template such as atemplate: (args)=>html'some text ${ args.named } does not appear to work and it's unclear if the indexed approach shown below is the only option available

thanks very much.

// templates has key with the template:
  check_email: html`checking ${ 0 }`, 
  ...
  check_email_does_not_work: (args)=>html`checking ${ args.address }`
// unclear how to make the above templates work, except for the index approach 0, 1... 
// and whether this is the only option available for logic in templates


const address = `user@host`; 
msg(str`checking...${address}`, {id:'check_email'})

// like
greeting: html`<b>Hola Mundo</b>`,
parameterized: html`<b>Hola ${0}</b>`,
htmlOrderChange: html`<b>2:${1} 1:${0}</b>`,

docs at:
https://lit.dev/docs/localization/overview/

current source of information in tests:
https://github.com/search?q=repo%3Alit%2Flit%20localize%20%7B0%7D&type=code
https://github.com/lit/lit/blob/a66737fc9b861999b00ccad01edb925172b7f711/packages/localize-tools/testdata/build-runtime-xliff/goldens/tsout/zh_CN.ts#L5