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In a right-to-left, top-to-bottom script (commonly shortened to right to left or abbreviated RTL), writing starts from the right of the page and continues to the left. This can be contrasted against left-to-right writing systems, where writing starts from the left of the page and continues to the right.
Right-to-left can also refer to top-to-bottom, right-to-left (TB-RL or TBRL) scripts such as Chinese, Japanese, and Korean, though they are also commonly written left to right. Books designed for predominately TBRL vertical text open in the same direction as those for RTL horizontal text: the spine is on the right and pages are numbered from right-to-left.
Arabic, Hebrew, Persian, and Urdu are the most widespread RTL writing systems in modern times. As usage of the Arabic script spread, the repertoire of 28 characters used to write Arabic language was supplemented to accommodate the sounds of many other languages such as Persian, Pashto, etc. While the Hebrew alphabet is used to write Hebrew language, it is also used to write other Jewish languages such as Yiddish.
Syriac and Mandaean (Mandaic) scripts are derived from Aramaic and are written RTL. Samaritan is similar, but developed from Proto-Hebrew rather than Aramaic. Many other ancient and historic scripts derived from Aramic and inherited its right-to-left direction.
Several languages have both Arabic RTL and non-Arabic LTR writing systems. For example, Sindhi is commonly written in Arabic and Devanagari scripts, and a number of others have been used. Kurdish may be written in Arabic, Latin, Cyrillic or Armenian script.
Thaana appeared around 1600 CE. Most modern scripts are LTR, but the African scripts N'Ko (1949), Mende Kikakui (19th century), Adlam (1980s) and Hanifi Rohingya (1980s) were created in modern times and are RTL.
Ancient examples of text using alphabets such as Phoenician, Greek, or Old Italic may exist variously in left-to-right, right-to-left, or boustrophedon order; so it is not always possible to classify some ancient writing systems as purely RTL or LTR.
Right-to-left, top-to-bottom text is supported in common consumer software. Often this support must be explicitly enabled. Right-to-left text can be mixed with left-to-right text in bi-directional text.
Examples of right-to-left scripts (with ISO 15924 codes in brackets) are:
Aran161) – used for Arabic, Persian, Urdu and many other languages.
Syrc135, variants 136–138
Syrn Syrj Syre) – used for varieties of the Syriac language.
Samr123) – closely related to Hebrew, used for the Samaritans' writings.
Mand140) – closely related to Syriac, used for the Mandaic language.
Thaa170) – used for Dhivehi.
Mend438) – for Mende in Sierra Leone. Devised by Mohammed Turay and Kisimi Kamara in the late 19th century. Still used but only by about 500 people.
Nkoo165) – devised for the Manding languages of West Africa.
Adlm166) – devised in the 1980s for writing the Fula languages of West and Central Africa.
Rohg167) — developed in the 1980s for the Rohingya language.
Hebr125) – used for Hebrew, Yiddish and some other Jewish languages.
Cprt403) – predates Phoenician influence.
Phnx115) – ancient, precursor to Hebrew, Imperial Aramaic, and Greek.
Armi124) – ancient, closely related to Hebrew and Phoenician. Spread widely by the Neo-Assyrian and Achaemenid empires. The later Palmyrene form (
Palm126) was also used to write Aramaic.
Prti Phli Phlp Phlv) – derived from Aramaic.
Avst134) – from Pahlavi, with added letters. Used for recording the Zoroastrian sacred texts during the Sassanid era.
Mani139, associated with the Manichaean religion) – derived from Syriac. Sogdian eventually rotated from RTL to top-to-bottom, giving rise to the Old Uyghur, Mongolian, and Manchu vertical scripts.
Nbat) – intermediate between Syriac and Arabic.
Khar305) – an ancient script of India, derived from Aramaic.
Ital210) – Early Etruscan was RTL but LTR examples later became more common. Umbrian, Oscan, and Faliscan were written right-to-left. Unicode treats Old Italic as left-to-right, to match modern usage. Some texts are boustrophedon 
Lydi116) – ancient; some texts are left-to-right or boustrophedon.
Most early Etruscan texts have right-to-left directionality. From the third century BCE, left-to-right texts appear, showing the influence of Latin. Oscan, Umbrian, and Faliscan also generally have right-to-left directionality. Boustrophedon appears rarely, and not especially early .... Despite this, for reasons of implementation simplicity, many scholars prefer left-to-right presentation of texts, as this is also their practice when transcribing the texts into Latin script. Accordingly, the Old Italic script has a default directionality of strong left-to-right in this standard. When directional overrides are used to produce right-to-left presentation, the glyphs in fonts must be mirrored ...