if u are among those people who love msging chat apart from whatsapp and fb messenger you would have surely known what the lock option is...for instance you are having a long conversation with a person xyz ..when u keep on chatting the older messages begin to disappear so as to make room for newer msgs. suppose you want a specific msg and dont want to loose it...in this case the lock option comes to aid...u can lock a particular msg so as to prevent it from disappearing.
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