Returns the result of following a numeric cell path (e.g. `$custom_value.0`) on the custom value. This is most commonly used with custom types that act like lists or tables. The argument is a spanned unsigned integer. The response type is [`PipelineData`](#pipelinedata-plugin-call-response) or [`Error`](#error-plugin-call-response). The result **may** be another custom value. If the operation produces a stream, it will be consumed to a value.

Example:

```nu
$version.0
```

```json
{
  "Call": [
    0,
    {
      "CustomValueOp": [
        {
          "item": {
            "name": "version",
            "data": [0, 0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0]
          },
          "span": {
            "start": 90,
            "end": 96
          }
        },
        {
          "FollowPathInt": {
            "item": 0,
            "span": {
              "start": 320,
              "end": 321
            }
          }
        }
      ]
    }
  ]
}
```

##### `FollowPathString`

Returns the result of following a string cell path (e.g. `$custom_value.field`) on the custom value. This is most commonly used with custom types that act like lists or tables. The argument is a spanned string. The response type is [`PipelineData`](#pipelinedata-plugin-call-response) or [`Error`](#error-plugin-call-response). The result **may** be another custom value. If the operation produces a stream, it will be consumed to a value.

Example:

```nu
$version.field
```

```json
{
  "Call": [
    0,
    {
      "CustomValueOp": [
        {
          "item": {
            "name": "version",
            "data": [0, 0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0]
          },
          "span": {
            "start": 90,
            "end": 96
          }
        },
        {
          "FollowPathString": {
            "item": "field",
            "span": {
              "start": 320,
              "end": 326
            }
          }
        }
      ]
    }
  ]
}
```

##### `PartialCmp`

Compares the custom value to another value and returns the [`Ordering`](#ordering) that should be used, if any. The argument type is a [`Value`](#value), which may be any value - not just the same custom value type. The response type is [`Ordering`](#ordering-plugin-call-response). [`Error`](#error-plugin-call-response) may also be returned, but at present the error is unlikely to be presented to the user - the engine will act as if you had sent `{"Ordering": null}`.

Example (comparing two `version` custom values):

```json
{
  "Call": [
    0,
    {
      "CustomValueOp": [
        {
          "item": {
            "name": "version",
            "data": [0, 0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0]
          },
          "span": {
            "start": 90,
            "end": 96
          }
        },
        {
          "PartialCmp": {
            "Custom": {
              "val": {
                "type": "PluginCustomValue",
                "name": "version",
                "data": [0, 0, 0, 0, 1, 0, 0, 0, 3, 0, 0, 0]
              },
              "span": {
                "start": 560,
                "end": 566
              }
            }
          }
        }
      ]
    }
  ]
}
```

##### `Operation`

Returns the result of evaluating an [`Operator`](#operator) on this custom value with another value. The argument is a 2-tuple: (`operator`, `value`), where `operator` is a spanned [`Operator`](#operator) and `value` is a [`Value`](#value), which may be any value - not just the same custom value type. The response type is [`PipelineData`](#pipelinedata-plugin-call-response) or [`Error`](#error-plugin-call-response). The result **may** be another custom value. If the operation produces a stream, it will be consumed to a value.

Example:

```nu
$version + 7
```

```json
{
  "Call": [
    0,
    {
      "CustomValueOp": [
        {
          "item": {
            "name": "version",
            "data": [0, 0, 0, 0, 1, 0, 0, 0, 2, 0, 0, 0]
          },
          "span": {
            "start": 90,
            "end": 96