wikipedia : Devnagari :- : "The avagraha ऽ (usually transliterated with an apostrophe) is a Sanskrit punctuation mark for the elision of a vowel in sandhi: एकोऽयम् ekoyam (< ekas + ayam) "this one". An original long vowel lost to coalescence is sometimes marked with a double avagraha: सदाऽऽत्मा sadātmā (< sadā + ātmā) "always, the self". Its main function is to show that a vowel is sustained in a cry or a shout:"
Do we have a similar feature in any other languages? How is the 'stretching' of a long vowel denoted in other languages ?