In articles, apostroph is frequently used. Generally, it deletes unstressed vowels when they meet another vowel (e.g. de aqua > d'aqua), but there are also other forms of elision (e.g. quater or > quatr'or). Normally, the words that use elision are articles, prepositions and personal pronouns. The article prepositions comes from an elision. El/la > l'; ona > on'; i and di do not elide. It's common also the elision of a vowel at the beginning of the word, specially when hard stress is far (e.g. ona>'na, el>'l).