The numbers that follow these letters represent the office of a particular department. For instance, all Internal Revenue Service publications will be given a number beginning with T 22. The numbers after the decimal point represent second and subsequent level offices.
Numbers immediately following the colon indicate numbered series, volumes or dates.
Letters and numbers immediately following the colon are based on a system which organizes materials alphabetically by subject. In general, documents are shelved in alphabetical and numerical order. This is not a decimal system. Numbers between punctuation are treated as individual whole numbers. LE 78 Numbers precede letters.