In confluent, any attribute may either be a straightforward value, or an expression to generate the value.

An expression will contain some directives wrapped in '{}' characters. Within {} are a number of potential substitute values and operations.

The most common operation is to extract a number from the nodename. These values are available as `n1`, `n2`, etc. So for example attributes for a node named b1o2r3u4 would have `{n1}` as 1, `{n2}` as 2, `{n3}` as 3, and `{n4}` as 4. Additionally, `{n0}` is special as representing the *last* number in a name, so in the b1o2r3u4 example, `{n0}` would be 4.

Frequently a value derives from a number in the node name, but must undergo a transform to be useful. As an example, if we have a scheme where nodes are numbered `n1-n512`, and they are arranged 1-42 in `rack1`, 43-84 in `rack2`, and so forth, it is convenient to perform arithmetic on the extracted number. Here is an example of codifying the above scheme, and setting the u to the remainder:

```
location.rack=rack{(n1-1)/42+1}
location.u={(n1-1)%42+1}
```

Note how text may be mixed into expressions, only data within {} will receive special treatment. Here we also had to adjust by subtracting 1 and adding it back to make the math work as expected.

It is sometimes the case that the number must be formatted a different way, either specifying 0 padding or converting to hexadecimal. This can be done by a number of operators at the end to indicate formatting changes.

```
{n1:02x} - Zero pad to two decimal places, and convert to hexadecimal, as might be used for generating MAC addresses
{n1:x} - Hexadecimal without padding, as may be used in a generated IPv6 address
{n1:X} - Uppercase hexadecimal
{n1:02d} - Zero pad a normal numeric representation of the number.
```

Another common element to pull into an expression is the node name in whole:

```
hardwaremanagement.manager={nodename}-imm
```

Additionally other attributes may be pulled in:

```
net.switchport={location.u}
```

Multiple expressions are permissible within a single attribute:

```
hardwaremanagement.manager={nodename}-{hardwaremanagement.method}
```

A note to developers: in general the API layer will automatically recognize a generic set attribute to string with expression syntax and import it as an expression. For example, submitting the following JSON:

```
{ 'location.rack': '{n1}' }
```

Will auto-detect `{n1}` as an expression and assign it normally. If wanting to set that value verbatim, it can either be escaped by doubling the {} or by explicitly declaring it as a value:

```
{ 'location.rack': '{{n1}}' }

{ 'location.rack': { 'value': '{n1}' } }
```