What is it?
<sourceDesc> element describes the source document, which is detailed in its child tag
In our case, the <bibl> element contains the actual description of the source. For example:
<sourceDesc> <bibl>abbreviated in the Manuscript Chronology as EN1<lb/><lb/> "Written in blue and red inks in three notebooks. Each notebook has, in Beckett's hand, the title, number of the notebook, and the note, 'original manuscript of the author's translation'. The second notebook has the additional phrase (title?) 'Beyond words?' The last manuscript page of the third notebook bears the inscription: 'This is the original MS of my translation of L'Innommable / For my friend Jake Schwartz, / with my best wishes. / Samuel Beckett / March 1958.'"<lb/><lb/> Lake, Carlton, ed. (1984), <hi rend="i">No Symbols Where None Intended: A Catalogue of Books, Manuscripts and Other Material Relating to Samuel Beckett in the Collections of the Humanities Research Center</hi> (Austin: Humanities Research Center), p. 62, item 112</bibl> </sourceDesc>