The core XBRL specifications (see XBRL Essentials) define validation constraints which XBRL processors must impose on all XBRL reports. These enforce not only basic syntactical checks, but also ensure that the reports comply with the definitions in the taxonomy. The validation checks include:

All XBRL concept definitions are associated with a datatype that enforces basic validation of the format of reported values. For example, ensuring that strings are not reported against concepts which should take numeric values. At a technical level, XBRL reuses the XML Schema datatype system. The standard defines a wide range of base datatypes, but the Data Type Registry 1.x allows for the collaborative development, rapid review, publication and on-going use of additional specialised data constraints.
Taxonomies can associate dimensions with concept definitions, thereby controlling which dimensions may - or must - be used with particular concepts.
Taxonomies can capture basic summation relationships between concepts which will be checked during the validation process. As the scope of calculations that can be defined in this way is limited, many implementations choose to use Formula for all calculation constraints.
The XBRL 2.1 specification requires that facts for concepts with a monetary datatype use particular units based on the ISO 4217 currency code standard. More general constraints between datatypes and units can be defined in the Units Registry 1.0.

Many reporting domains have a need to impose more complex constraints on reported data. For example, the value of one reported fact may control whether another fact is required, or there may be more calculation constraints between facts.

The Formula specification makes it possible to capture such constraints in an XBRL taxonomy in a standardised format. This makes XBRL taxonomies immensely powerful, as a regulator can publish a single artefact that completely defines the reporting requirements for a particular domain including validation rules that can be executed by any conformant software.