1. A computer-implemented method, comprising: receiving an input sequence of one or more alphabet characters; identifying one or more candidate sequences that satisfy predefined usage frequency criteria with respect to the input sequence, each candidate sequence comprising a concatenation of the input sequence and one or more additional alphabet characters, wherein: the candidate sequences include partial words; and the identifying one or more candidate sequences that satisfy predefined usage frequency criteria comprises: identifying a character sequence tree data structure, each node of the character sequence tree corresponding to a distinct character sequence, the input sequence corresponding to a first node in the character sequence tree; and selecting one or more candidate character sequences corresponding to one or more descendent nodes of the first node that have values above a predefined threshold, wherein a respective value for a respective descendent node of the first node is the usage frequency weight of the respective descendent node divided by the usage frequency weight of the first node; and presenting a candidate sequence from the one or more identified candidate sequences that is a partial word, wherein the partial word comprises a concatenation of the input sequence and two or more additional alphabet characters and the partial word by itself is not a complete word.