A method and system for checking the validity of a sequence of input characters according to the syntactical rules of a selected language is provided. If an input character may not begin a valid sequence of characters, or if the input character may not be appended to a previously input sequence of characters according to the rules of the selected language, the newly input character may be prohibited from being displayed singularly or appended to the previous sequence and displayed on the user's computer. Previously input character sequences may be edited by determining the sequence validity context of previously input sequences of characters.