title: MacroInternals

Macros are conventional JavaScript modules that export a single variable called `macro` that contains:

|!Field Name |!Description |
|`name` |The name of the macro |
|`types` |An array of the MIME types that the macro can render |
|`params` |A hashmap of the parameters accepted by the macro (see below) |
|`handler` |The macro rendering function (see below) |

The `params` hashmap provides the following fields about each parameter:

|!Param Field Name |!Description |
|`byName` |Provided if the parameter should be referenced by name. The value can be `true` or `"default"` to indicate that the parameter should accept anonymous parameters |
|`type` |The type of the parameter, from `text` or `tiddler` (used for dependency tracking) |
|`optional` |`true` if the parameter is optional |

The `code` function is called with the following parameters:

|!Param Name |!Description |
|`type` |The target MIME type for rendering the macro |
|`tiddler` |The tiddler in whose context the macro is being rendered |
|`store` |The `WikiStore` object to be used |
|`params` |The macro parameters as a hashmap |
|`content` |The rendered text of the children of the macro |