uRrite by rule 4
try here
* There are five different ways that new words can be formed:
1. Adding one or more tiles to the beginning or end of a word already on the board, or to both the beginning and end of that word.
e.g. Trainer can become Strainers if you have two tiles with the letter S.
2. Placing a word at right angles to a word already on the board. The new word must use one of the letters of the word already on the board. Note, a right angle can be _| or |_
3. Placing a complete word parallel to a word already played so that adjoining tiles also form complete words.
4. A new word added at right angles can also add a letter to an existing word.
5. The last variation is to bridge two or more letters. (This can only be done after the fourth move or later in the game).