How does the author use foreshadowing in Euripides V?

In the play, Electra, Orestes disguises himself as a stranger to find out the situation and Electra's feelings before he reveals himself. Electra's comment that Agamemnon's old servant would recognize Orestes foreshadows the revelation of Orestes' identity. The fact that even Electra cannot recognize her brother also foreshadows the future, when Orestes passes unnoticed among his enemies later in the play.