The way Create mod currently handles displaying information (let's call one an input string) with the attached label is by simply concatenating both with a space in between -
it's a simple way, but thus, in terms of customization, a severely limiting one:

This add-on pushes the boundaries apart by introducing the $ and {} placeholders.
Placing one (or more) marks the place where the input string should be inserted.
In short, the Attached Label can now act like a formatted string!

You can utilize as many placeholders as you want in one string. Mixing both types of them doesn't cause any issues as well!

If you need to insert a $ character literally (same applies to {}), without it turning into a placeholder, use backslash-escaping on it.

In case of no unescaped placeholders present in the label altogether, default (base Create's) concatenation will be applied.

Lastly, there's a new hover-on button that displays a Placeholders Usage Guide tooltip containing all the abovementioned.

Its last string displays which placeholders are active (available to use in this world/server, which is specified by the server config of the mod).

Client settings

• Enable Guide Buttons: toggling that off will hide the abovementioned hover-on button in the Display Link interface.
• Tooltip Customization:
  • Enable (Active Placeholders / Progress Bar Support) Tooltip: those two add their additional strings into the Placeholders Usage Guide tooltip, that change the text, reflecting the states of their respective config options in Server settings.

Server settings

• Hide Escaping Of Disabled Placeholders: by default, when a disabled placeholder is escaped, the backslash stays visible as if placed before a regular character; enable to make it get hidden like if it did its job;
• Enable Crude Progress Bar Support: currently the progress bar characters are being rendered incorrectly (appear squashed together) if used with placeholders, so the support for this display format is disabled altogether by default (see Known Issues).
• Placeholders Availability:
  • Enable (Dollar Sign / Curly Brackets) Placeholder: with those two it is possible to limit the placeholder functionality to only one option - the Dollar Sign or the Curly Brackets respectively - or disable the feature altogether by ticking both as off (affects the last string of the Placeholders Usage Guide tooltip);