Setting the value for the name attribute with cforms input fields

I found it. Under the Core Form Admin sections in the options, there’s an option called Use custom input fields names & ids, with the following note:

This feature replaces the default NAMEs/IDs (e.g. cf_field_12) with custom ones, either derived from the field label you have provided or by specifically declaring it via [id:XYZ],e.g. Your Name[id:the-name]. This will for instance help to feed data to third party systems (requiring certain input field names in the $_POST variable).