# rule_variable · FT4 Rell API · Chromia Docs (concept)

> enum rule_variable Similar to accounts.rule_variable , but it adds two more variables that only make sense
in the context of login auth descriptors: relati

Source: https://docs.chromia.com/pages/ft4-rell/-f-t4-library/lib.ft4.core.auth/rule_variable/

ENUM

# rule\_variable

```signature
enum rule_variable
```

[Source](https://gitlab.com/chromaway/ft4-lib/-/blob/development/rell/src/lib/ft4/core/auth/login.rell#lines-153)

Similar to `accounts.rule_variable`, but it adds two more variables that only make sense
in the context of login auth descriptors:

* `relative_block_time` is the difference in timestamp between the auth descriptor creation
  and its expiration
* `relative_block_height` is the difference in block number between the auth descriptor
  creation and its expiration

These two variables are not useful for normal auth descriptors, as those are created at
the same time of definition.
In the case of login auth descriptors, the definition happens during the dapp development,
while they're created anytime a user logs in. This allows the developer to define rules
like a time to live for the login sessions.

**See Also**

* `core.accounts.rule_variable` — for more information on rule variables
* `core.accounts.rule_expression` — for more information on expiration rules

## Entries

`block_height`

`block_time`

`op_count`

`relative_block_height`

`relative_block_time`

[View this page on docs.chromia.com](https://docs.chromia.com/pages/ft4-rell/-f-t4%20-library/lib.ft4.core.auth/rule_variable/index.html)Generated API reference, mirrored from the live docs