The parameter to a filter operator can be:

hard

[like this]

The parameter is the exact text that appears between the square brackets.

soft

indirect

{like this}

The parameter is the text indicated by the text reference whose name appears between the curly brackets, i.e. a field of a specified tiddler, or the value of a property of a specified data tiddler.

variable

<like this>

The parameter is the current value of the variable whose name appears between the angle brackets. Macro parameters are not supported up to and including TiddlyWiki v5.1.23.

New in: 5.2.0 Literal macro parameters are supported. For example: [<now [UTC]YYYY0MM0DD0hh0mm0ssXXX>].

New in: 5.1.23 Filter operators support multiple parameters which are separated by a , character.

For example: [param1],[param2] or <param1>,{param2}