This schema specifies the format for vocabulary lists. Lists occur in special-purpose documents containing nothing else, that are made accessible on the internet. BrainML instance documents may refer to these by use of a 'vocab' element that is defined in the main BrainMetaL schema. They may NOT define vocabulary themselves. If terms need to be added, a schema authority should submit a vocabulary definitions document to the schema repository. A 'domain' describes the content domain a term applies to. Domains may be nested to create subdomains, sub-subdomains, etc.. This is the identifier by which the domain will be referenced. Valid characters in identifiers are ONLY letters, numbers, underscore, period, and dash, and an identifier cannot start with a number. The identifier for a domain should be unique within its containing document among both domains and terms. By convention, this ID should be an underscore followed by a number beginning with 1,2,3, or 4. This should be added automatically by the VocabConverter tool, and if you are hand-editing a file just put "_". This is the simple name of the domain, without any hierarchy or context. Description of the domain's meaning and intended usage. (Optional) Used to link a controlled vocabulary term with an equivalent term or definition in another system, such as the UMLS. BrainML does not explicitly support structured term definition, but through linking to another system that does, existing semantic structure can be maintained when metadata is expressed in BrainML. A 'term' is an atomic descriptor that exists in an ISA hierarchy and is associated with a particular domain of applicability. This is the identifier by which the term will be referenced. Valid characters in identifiers are ONLY letters, numbers, underscore, period, and dash, and an identifier cannot start with a number. The identifier for a term should be unique within its containing document among both domains and terms. By convention, this ID should be an underscore followed by a number beginning with 5,6,7 or 8. This should be added automatically by the VocabConverter tool, and if you are hand-editing a file just put "_". This is the simple name of the term, without any hierarchy or context. Description of the term's meaning and intended usage. (Optional) It is not fully decided whether the ISA hierarchy is a tree or a DAG in which a term may have multiple parents. In the latter case, the term actually would occur in two or more different places in the XML element hierarchy with the same name but different IDs. One or more 'internal-equivalent' children is used to link each instance of the term to all the others. This approach is similar to that used in the HDF5 XML format to represent directed graphs. (see http://hdf.ncsa.uiuc.edu/HDF5/XML/design-notes.html) This is the top-level element for a document listing term declarations.