A label is said to be well formed if it follows a specified set of rules regarding the relationships among classifications and words in the same label. The concept of well formedness applies to information labels, sensitivity labels, and clearances. The encodings and their associated software that translates human-readable labels into their internal format enforces the following types of well formedness rules.
A set of "default words" can be associated with 1) the least sensitive clearance and sensitivity label, and/or 2) the least sensitive information label, containing a particular classification. Such words are defined by including the compartment and/or marking bits associated with them in the initial compartments and/or initial markings associated with the classification. See the initial compartments= and initial markings= keywords in Classification Encodings. For example, if all classified data on a particular system was to be considered NOFORN (meaning No Foreign Dissemination), and NOFORN was an information label word (i.e., has marking bits associated), then NOFORN could be encoded as a default word for all classifications above UNCLASSIFIED, and would therefore automatically appear in all information labels.
A minimum classification can be associated with each word, thereby preventing the word from appearing in the human-readable form of a label with a classification below the minimum. See the minclass= keyword in Information Label Encodings. For example, the minimum classification that should be associated with some compartments is TOP SECRET.
An "output minimum" classification can be associated with each word, thereby preventing the word from appearing in the human-readable form of a label with a classification below the minimum, even though it can appear in the internal form of the label. See the ominclass= keyword in Information Label Encodings. For example, release markings do not appear in the human-readable form on the label UNCLASSIFIED, and therefore have an output minimum classification of CONFIDENTIAL.
An "output maximum" classification can be associated with each word, thereby preventing the word from appearing in the human-readable form of a label with a classification above the maximum, even though it can appear in the internal form of the label. See the omaxclass= keyword in Information Label Encodings.
A maximum classification can be associated with each word, thereby preventing the word from appearing in a label with a classification above the maximum. See the maxclass= keyword in Information Label Encodings. For example, see the codeword bravo4 in Annotated Sample Encodings.
Any specific set of words can be defined to be in a hierarchy, such that only one word in the hierarchy can appear in a label at a time. The hierarchies among words are defined by the compartment and/or marking bits chosen to represent the words internally. Simply stated, if the compartment and marking bits associated with word W2 dominate but do not equal those associated with word W1, then W2 is in a hierarchy above W1, in which case W1 and W2 can never appear in a label together. See the compartments= and markings= keywords in Information Label Encodings and Hierarchies of Words in Enforcing Proper Label Adjudications. For example, see the codewords alpha1, alpha2, and alpha3 in Annotated Sample Encodings.
The presence of any word in a label can require the presence of another word in the same label. See the REQUIRED COMBINATIONS: keyword in Information Label Encodings. For example, certain subcompartments may require the presence of their main compartment in a sensitivity label.
Some words can be prevented from appearing with other words in the same label, even if the words are not hierarchically related. See the COMBINATION CONSTRAINTS: keyword in Information Label Encodings. For example, the codeword bravo4 in Annotated Sample Encodings must stand-alone in a label.