--- title: --- The `` element allows you to specify compiler options. We'll use the `immutable` option as an example. In this app, the `` component flashes whenever it receives new data. Clicking on one of the items toggles its `done` state by creating an updated `todos` array. This causes the _other_ `` items to flash, even though they don't end up making any changes to the DOM. We can optimise this by telling the `` component to expect _immutable_ data. This means that we're promising never to _mutate_ the `todo` prop, but will instead create new todo objects whenever things change. Add this to the top of the `Todo.svelte` file: ```svelte ``` > You can shorten this to `` if you prefer. Now, when you toggle todos by clicking on them, only the updated component flashes. The options that can be set here are: - `immutable={true}` — you never use mutable data, so the compiler can do simple referential equality checks to determine if values have changed - `immutable={false}` — the default. Svelte will be more conservative about whether or not mutable objects have changed - `accessors={true}` — adds getters and setters for the component's props - `accessors={false}` — the default - `namespace="..."` — the namespace where this component will be used, most commonly `"svg"` - `customElement="..."` — the name to use when compiling this component as a custom element Consult the [API reference](/docs) for more information on these options.