Sentence:  The <WSD>speaker</WSD> spelled out the words to be communicated, letter by letter, while the reader's hand read the speaker's message. In its original form the hand alphabet assumed that both <WSD>speaker</WSD> and reader could already speak and spell the words ... 
Meaning of the word marked with <WSD> tags:  (linguistics)  The producer of a given utterance (text, etc), whether actually spoken or e.g. written.