# Expression selector

Learn how to get values using dynamic expressions.

The expression selector is the most versatile, as it allows you to use any expression to access a property or an item in a [list](/reference/cql/data-types/core/collection#list).

This selector is especially useful when the property name is not a [valid identifier](/reference/cql/syntax#identifiers) or when you want to dynamically compute the index or key.

For example, say you want to get the value of a query string parameter named `referral code`. Because the property name contains spaces, you can only access it using the expression selector:

```cql
page.query['referral code']
```

Because you can use any expression, you could store the property name in a variable and use it in the expression:

```cql
let param = 'referral code';

page.query[param]
```

You can also use numeric indexes to access items in a list:

```cql
let transport = ["🚀", "🚗", "🚆"];

transport[0] // 🚀
```

Notice that the index is zero-based, so the first item has an index of `0`, the second item has an index of `1`, and so on. For a more natural way to access items in a list, see the [ordinal selector](/reference/cql/expressions/accessors/bracket/selectors/ordinal).

## Explore

- [Dot notation](/reference/cql/expressions/accessors/dot): Learn how to access properties using dot notation.
- [Ownership notation](/reference/cql/expressions/accessors/ownership): Learn how to access properties using the apostrophe-s notation.