Our initiative aims at designing a controlled vocabulary for the description of the layout of textual sources: SegmOnto. Following a codicological approach rather than a semantic one, it is designed as a generic typology, coping with a maximal number of cases rather than answering specific needs. The harmonisation of the layout description has a double objective: on the one hand it facilitates the mutualisation of annotated data and therefore the training of better models for image segmentation (a crucial preliminary step for text recognition), on the other hand it allows the development of a shared post-processing workflow and pipeline for the transformation of ALTO or PAGE files into DH standard formats, which preserves as much as possible the link between the extracted information and the digital facsimile.