Letters served as numerals as well as phonetic signs the values of the numerals were directly borrowed from their Greek-letter analogues.
There was no distinction of capital and lowercase letters, though manuscript letters were rendered larger for emphasis, or in various decorative initial and nameplate forms. It is also violated by a significant failure to distinguish between /ji/ and /jĭ/ orthographically. Particularly, this principle is violated by certain vowel letters, which represent plus the vowel if they are not preceded by a consonant.
The Cyrillic alphabet was very well suited for the writing of Old Church Slavic, generally following a principle of "one letter for one significant sound", with some arbitrary or phonotactically-based exceptions. One possibility is that this systematization of Cyrillic was undertaken at the Council of Preslav in 893, when the Old Church Slavonic liturgy was adopted by the First Bulgarian Empire. An alternative hypothesis proposes that it emerged in the border regions of Greek proselytization to the Slavs before it was codified and adapted by some systematizer among the Slavs the oldest Cyrillic manuscripts look very similar to 9th and 10th century Greek uncial manuscripts, and the majority of uncial Cyrillic letters were identical to their Greek uncial counterparts. Cyrillic, on the other hand, was a creation of Cyril's students in the 890s at the Preslav Literary School as a more suitable script for church books, based on uncial Greek but retaining some Glagolitic letters for sounds not present in Greek. The Glagolitic alphabet was created by the monk Saint Cyril, possibly with the aid of his brother Saint Methodius, around 863. The earliest form of manuscript Cyrillic, known as ustav, was based on Greek uncial script, augmented by ligatures and by letters from the Glagolitic alphabet for consonants not found in Greek. 4.2 Medieval Greek Uncial manuscripts from which early Cyrillic letter forms take their shapes.