Templates: Where are "placeholders" and their values defined?

[martinboers]

In this section of the Wiki:

https://github.com/PLCnext/PLCnext_CLI/wiki/Template-System#11placeholder-syntax

... it states:

In the PLCnCLI Template System, placeholders are denoted using the $(path.to.value) syntax. This notation allows the user to specify the path to the desired value in a hierarchical data structure. The path is evaluated by the PLCnCLI, and the corresponding value is inserted into the output file at the position of the placeholder.

The example includes the following placeholders:

$(file.name)
portStructs [in the foreach loop]
$(struct.file.format.include)
$(file.format.include)
$(file.namespace)
file.functions [in the foreach loop]
$(function.name)
function.hasImplementation
$(function.implementation)

It's not clear to me where these placeholders and their values are defined.

Is there a pre-defined set of placeholders, like "file", for all templates? If so, where can I see this set of placeholders?

Or, does each template need to define its own complete set of placeholders? If so, where and how is that done?