Digital Manuscripts can provide insight into a writer's process. Manuscript collections can often be found by Googling the author's name and the phrase "digital manuscripts."
Emily Dickinson manuscript excerpt, poem #935 "As imperceptibly as grief"
Amherst College, Emily Dickinson Collection
Literature Criticism Online is a good starting place for critical analysis of an author and their work:
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Subject: Theatre Arts, Literature Literary criticisms, biographies of authors, reference resources, plus works of poetry, drama, and prose fiction from the sixth century to the present day.
To find essays of critical analysis on an author or work, add the words and criticism to an author's name or the title of a work. For example: Robert Frost and criticism OR Paradise Lost and criticism