## 2 Theoretical Background
### TPACK Framework  
The TPACK framework by [PERSON] and [PERSON] [16] extends [PERSON]'s [40] seminal pedagogical content knowledge framework by adding technological knowledge and the resulting intersections. These intersections are known as technological content knowledge (TCK), technological pedagogical knowledge (TPK), and technological pedagogical and content knowledge (TPACK). Figure 1 illustrates the framework in the form of a Venn diagram [39]. Technological knowledge is conceptualized as developmental knowledge evolving according to technological changes. It encompasses teachers' knowledge, enabling them to accomplish various tasks using technology. TCK refers to the reciprocal relationship between content and technology. Teachers must learn how technology can alter, enhance, or hinder the learning of (subject-specific) content and how integrating technology can change the subject matter. Although not explicitly mentioned in the framework, TCK is one component when \"selecting dLMs\" for specific learning content. TPK refers to technology integration in teaching and learning processes and the knowledge of how various technologies impact such processes. In the definition of the TPK component, the authors also explicitly address the selection of digital resources in general as follows: \"...the ability to choose a tool based on its fitness, strategies for using the tool's affordances, and knowledge of pedagogical strategies...\" (p. 1028, [16]). TPACK, the key component that brings everything together, encompasses teachers' knowledge of the challenges and changes in teaching when using technology. This includes the knowledge of what makes content-related concepts easier or more challenging to learn and ways to overcome learning difficulties by using technology [16]. Although \"selecting dLMs\" is not explicitly addressed in the description of the TPACK component, one can deduce that this activity is included, as the selection process requires knowledge of the intersections of all components. Therefore, the facet of digital competence \"selecting dLMs\" is positioned within the TPACK component (see Figure 1). Figure 1: TPACK framework adapted from [PERSON] et al. [39] and the facet of “selecting dLMs”. Content knowledge is described as knowledge of the learning content, the curriculum knowledge regarding the learning content, and the special needs of learners [40]. The literature suggests that subject-specific content knowledge is essential when selecting dLMs [11; 33; 41]. Although the TPACK model's naming and terms are described as knowledge, the research community understands that they are more than knowledge and entail attitudes and skills, which therefore describe competences [11; 33; 34; 42; 43]. Nevertheless, we follow the naming convention established by [PERSON] et al. [39] and refer to the framework and the intersection of all three components (i.e., content, pedagogical, and technological knowledge) as TPACK. For developing \"selecting dLMs\" and designing items for its assessment, the TPACK framework and the descriptions of the CK, TCK, TPK, and TPACK components are essential. (1) Reasoning when \"selecting dLMs\" requires an understanding of the learning content with regard to the learner's age and the special needs of learners. (2) Justification when selecting dLMs can involve subject-specific TCK, subject-unspecific TPK, and TPACK reasoning. (3) Furthermore, reasoning when selecting dLMs can also be categorized as TCK, TPK, and TPACK reasoning. (4) There is not necessarily a single decision for selecting dLMs across different teaching situations and contexts. Thus, the reasoning behind the selection, rather than the decision itself, is essential when assessing \"selecting dLMs\". The following sections provide examples of TCK and TPK reasoning when \"selecting dLMs\".