Three Aztec codices have been considered as being possibly pre-Hispanic: Codex Borbonicus, the Matrícula de Tributos and the Codex Boturini. According to Robertson, no pre-Conquest examples of Aztec codices survived, for he considered the Codex Borbonicus and the Codex Boturini as displaying limited elements of European influence, such as the space apparently left to add Spanish glosses for calendric names in the Codex Borbonicus and some stylistic elements of trees in Codex Boturini. Similarly, the Matrícula de Tributos seems to imitate european paper proportions, rather than native ones. However, Robertson's views, which equated Mixtec and Aztec style, have been contested by Elizabeth-Hill Boone, who considered a more naturalistic quality of the Aztec pictorial school. Thus, the chronological situation of these manuscripts is still disputed, with some scholars being in favour of them being prehispanic, and some against.