The types of references (that is, citation sources) are identified by a single letter, as follows: m-monograph c-collection of papers n-newspaper article j-journal article d-paper r-report. For files that do not belong to the above types, use the letter "z" to identify them.

There are several kinds of numbers, and Arabic numerals are the most common one. Arabic numerals were not invented by Arabs, but by Indians. In fact, it should be listed as Hindi, but it spread to Arabia first and then to the world, so it is called "Arabic numerals". Numbers are written symbols used to represent numbers. Different counting systems can use the same number.