Michael Everson wrote:

> Abjad. A writing system in which only consonants are indicated. The
> Phoenician script is a prototypical abjad; a better-known example is
> the Arabic writing system, though it is not a "pure" abjad because
> consonant letters like /w/ and /y/ are used to mark long vowels /o/
> or /u/ or /i/.

Oblique bars usually denote phonemic notation, but [o:] is not an
independent phoneme in Arabic: it is an allophone of phoneme /u:/ (or of
diphthong /aw/).

Moreover, I'd substitute /w/ and /y/ with letter names in the form used
throughout the Unicode book.

«though it is not a "pure" abjad because consonant letters like ALEF, WAW
and YEH are used to mark long vowels /ā/, /ī/ or /ū/.»

--
Marco