command for biplot scaling in Factoextra

[rudybenetti]

Hi,
I've staretd to prificiently use your Factoextra package for PCA visualization, I like it very much, is intuitive and charts are beautiful. Just I have an issue in figuring out how to decide which kind of biplot your package launch as a defalut and, in case, change it. Namely, when I run the code viz_pca_biplot I'm not able to find a command for deciding the type of scaling process I want, if a correlation (alpha=0), better for variables, or distance (alpha=1), better for observations, biplot (see Zuur et al., 2007, pp. 201-204).
Therefore I would like to know:

1. which is the default scaling process in the viz_pca_biplot snippet?
2. is there a command to change it?

Thank you in advance for your clarification :)