A writing system is any conventional method of visually representing verbal communication. While both writing and speech are useful in conveying messages, writing differs in also being a reliable form of information storage and transfer. The processes of encoding and decoding writing systems involve shared understanding between writers and readers of the meaning behind the sets of characters that make up a script. Writing is usually recorded onto a durable medium, such as paper or electronic storage, although non-durable methods may also be used, such as writing on a computer display, in sand, or by skywriting. The general attributes of writing systems can be placed into broad categories such as alphabets, syllabaries, or logographies. Any particular system can have attributes of more than one category. In the alphabetic category, there is a standard set of letters (basic written symbols or graphemes) of consonants and vowels that encode based on the general principle that the letters (or letter pair/groups) represent speech sounds. In a syllabary, each symbol correlates to a syllable or mora. In a logography, each character represents a word, morpheme, or other semantic units. Other categories include abjads, which differ from alphabets in that vowels are not indicated, and abugidas or alphasyllabaries, with each character representing a consonant–vowel pairing. Alphabets typically use a set of 20-to-35 symbols to fully express a language, whereas syllabaries can have 80-to-100, and logographies can have several hundreds of symbols. Most systems will typically have an ordering of its symbol elements so that groups of them can be coded into larger clusters like words or acronyms (generally lexemes), giving rise to many more possibilities (permutations) in meanings than the symbols can convey by themselves. Systems will also enable the stringing together of these smaller groupings (sometimes referred to by the generic term 'character strings') in order to enable a full expression of the language. The reading step can be accomplished purely in the mind as an internal process, or expressed orally. A special set of symbols known as punctuation is used to aid in structure and organization of many writing systems and can be used to help capture nuances and variations in the message's meaning that are communicated verbally by cues in timing, tone, accent, inflection or intonation. A writing system will also typically have a method for formatting recorded messages that follows the spoken version's rules like its grammar and syntax so that the reader will have the meaning of the intended message accurately preserved. Writing systems were preceded by proto-writing, which used pictograms, ideograms and other mnemonic symbols. Proto-writing lacked the ability to capture and express a full range of thoughts and ideas. The invention of writing systems, which dates back to the beginning of the Bronze Age in the late Neolithic Era of the late 4th millennium BC, enabled the accurate durable recording of human history in a manner that was not prone to the same types of error to which oral history is vulnerable. Soon after, writing provided a reliable form of long distance communication. With the advent of publishing, it provided the medium for an early form of mass communication. Secure written communications were also made more reliable with the invention of encryption. The creation of a new alphabetic writing system for a language with an existing logographic writing system is called alphabetization, as when the People’s Republic of China studied the prospect of alphabetizing the Chinese languages with Latin script, Cyrillic script, Arabic script, and even numbers, although the most common instance of it, converting to Latin script, is usually called romanization.