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### `exists:`

This expression returns `true` if the path specified after it exists, and `false` otherwise. It is analogous to PHP's `isset()`.

Normally using a path which doesn't exist throws an error like "Cannot find variable ' `foo`' in current scope". Thus, uncertain paths must be checked first:

                <span tal:condition="exists:user/preferences" tal:content="user/preferences">
      Use user/preferences here if defined
    </span>

#### Tip

In PHPTALES use `isset()` instead.

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