Property sets in Juniper Apstra are collections of key-value pairs, typically in JSON format, that function as variables. Their primary purpose is for variable substitution within Jinja2 templates, most commonly used in configlets. When a configlet that references a property set is imported into a blueprint, the property set must also be imported to make the variables available. For modularity, a single configlet can be designed to reference and utilize variables from multiple different property sets simultaneously, allowing for flexible and reusable configuration templates.

C. Property sets are also used in Intent-Based Analytics (IBA) probes, not just configlets, for defining dynamic or reusable probe parameters.

D. The syntax for creating a property set is standard JSON (key-value pairs), which is a vendor-agnostic format defined within Apstra itself.

1. Juniper Apstra User's Guide, "Design > Configlets". This section explains that configlets use Jinja2 templating and can reference property sets for variable substitution. It also shows the workflow of importing both configlets and their associated property sets into a blueprint.

2. Juniper Apstra User's Guide, "Property Sets". This section details the creation and management of property sets, stating, "Property sets are collections of key/value pairs that are used for variable substitution in configlets and IBA probes." This confirms their use beyond just configlets.