Yo (Cyrillic) part of Russian alphabet
Yo, Jo, Io, or just Ë  (Ё ё; italics: Ё ё; Russian pronunciation: [jɵ]) is a letter of the Cyrillic script. In Unicode, the letter ⟨Ё⟩ is named CYRILLIC CAPITAL/SMALL LETTER IO.
In English, the letter Yo is romanized using the Latin ë (according to the ALA–LC and British Standards), ë (yë word-initially) (BGN/PCGN) or yo/jo (orthographic transcription) for Russian, and as i͡o (ALA–LC), yo (BGN/PCGN), or ë (BSI) for Belarusian. In international systems, Yo is romanized as ë (ISO 9).
It was derived from the Cyrillic letter Ye (Е е).Russian
The letter Yo or Jo is the seventh letter of the alphabet, but although it indicates a distinct sound from Ye, it is often treated as the same letter for alphabetisation and sorting. In the dictionary, ёж (hedgehog) comes after едо́к (eater) and before е́здить (to go).
⟨Ё⟩ represents the phoneme /o/ after /j/ or a soft consonant (or occasionally after ⟨ж⟩, ⟨ш⟩), and it should always be stressed. It alternates with ⟨е⟩, written in non-stressed positions. Unstressed ⟨ё⟩ appears only in rare loanwords, in compound words (in this case it may be considered to have secondary stress; most notably, ⟨ё⟩ occurs in words containing the prefixes трёх- 'three-' and четырёх- 'four-'), in derivatives of the name of the letter ⟨ё⟩ itself (ёфика́тор - yoficator), in loanwords (кёнигсбе́ргский - adjective from Königsberg, сёрфинги́ст from surfing - surfer, сёдзё - shōjo, гёмбёц - gömböc).
In modern Russian, the reflex of Common Slavonic /e/ under stress and following a palatalized consonant but not preceding a palatalized consonant is /o/. Compare, for example, Russian моё mojo ("my" neuter nominative and accusative singular) and Polish/Czech/Slovak/Serbo-Croatian/Slovenian moje. However, since the sound change took place after the introduction of writing, the letter ⟨е⟩ continued to be written in that position. It was not until the 18th century that efforts were made to represent the sound in writing.
From the mid-1730s, it appears sporadically as ⟨іо⟩ or ⟨і͡о⟩. This digraph and new letter ⟨ґ⟩ for the sound /ɡ/ were proposed to be added to the official alphabet in 1783 at a session of the Russian Academy under the presidency of Princess Yekaterina Romanovna Vorontsova-Dashkova, but both propositions were rejected by the academicians and the Metropolitan of Novgorod and Saint Petersburg Gavriil. At that time, the sounds /jo/—/ʲo/ and /ɡ/ were common in everyday Central Russian speech, but Church-Slavonic-styled pronunciation with /je/–/ʲe/ and /ɣ/ was preferred when reading literary texts.
The sounds [jo] (and [o] after soft consonants) that developed in Russian pronunciation, for a long time were not distinguished from [je] (and [e] after soft consonants) in writing. In the mid-18th century, a ligature in the form of the letters IO with a top joiner was introduced, but it was cumbersome and used rarely. Other variants in use were: о, ьо, їô, ió, ио.
In 1797, instead of existing options, the letter "Ё" was created by Russian Imperial historian, writer, poet and critic Nikolay Mikhailovich Karamzin. It was used for the first time in the 2nd book of "Aonides" in his poem "Sophistiated Solomon's Wisdom, or Thoughts Selected from Ecclesiastes" to create a rhyme between the words слёзы [ˈslʲɵzɨ] and розы [ˈrozɨ]. In other places of the poem he used the spelling слезы [ˈslʲezɨ].The diaeresis ◌̈ does not appear above any other letter in Russian. It serves no purpose except to differentiate between ⟨е⟩ and ⟨ё⟩.
Except for a brief period after World War II, the use of ⟨ё⟩ was never obligatory in standard Russian orthography. By and large, it is used only in dictionaries and in pedagogical literature intended for children and students of Russian as a second language. Otherwise, ⟨е⟩ is used, and ⟨ё⟩ occurs only when it is necessary to avoid ambiguity (such as to distinguish between все ("everybody") and всё ("everything") when it is not obvious from the context) or in words (principally proper nouns) whose pronunciation may not be familiar to the reader. Recent recommendations (2006) from the Russian Language Institute are to use ⟨ё⟩ in proper nouns to avoid an incorrect pronunciation. It is permitted, however, to mark ⟨ё⟩ whenever it occurs, which is the preference of some Russian authors and periodicals.
The fact that ⟨ё⟩ is frequently replaced with ⟨е⟩ in print often causes some confusion to both Russians and non-Russians, as it makes it more difficult for Russian words and names to be transcribed. One recurring problem is with Russian surnames, as both -ев (-ev/-yev) and -ёв (-yov/-ov) are common endings. Thus, the English-speaking world knows two leaders of the former Soviet Union as Khrushchev and Gorbachev, but their surnames end in Russian with -ёв, better transcribed -yov/-ov (which is why many English-speakers pronounce these names as if they end in -ov but they spell them with -ev).
The advent of the computer has had a great influence on the process of substitution ⟨ё⟩ with ⟨е⟩ for a counterintuitive reason: currently, the Russian alphabet contains 33 letters including ⟨ё⟩, and codepage designers usually prefer to omit ⟨ё⟩ so that all Russian letters can be placed into sections of 16 letters (16, like other powers of 2, is often preferred in computing over other numbers). Some examples are pre-Unicode character pages 866 for Microsoft DOS and 1251 for Microsoft Windows. Since in both cases, ⟨ё⟩ was placed outside its alphabetically correct position, it made text sorting more complex. Software developers would then choose to substitute all ⟨ё⟩ letters with ⟨е⟩ at an early stage of text processing to simplify later stages.
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