Fig. 1

Timeline for the conceptualization of DL

Note: The dates for the European Union definitions refer to the publication year of the corresponding recommendations (2006 and 2018), being the final publication of the reports a year later, which corresponds to the references cited in the text (European Commission, 2019; European Communities, 2007). This figure has been created based on the information provided by several of the reviews for the conceptualization of DL (Avello Martínez et al., 2013; Canchola-Gonzalez & Glasserman Morales, 2020; Gibson & Smith, 2018; Manca et al., 2021; Perdomo et al., 2020; Reddy et al., 2020; Reis et al., 2019; Reyes & Avello-Martínez, 2021).