.ch is Switzerland: https://en.m.wikipedia.org/wiki/.ch

Obviously /s

Adolescents attending schools with restrictive, compared to permissive policies had lower phone (adjusted mean difference −0.67 h, 95% CI −0.92 to −0.43, p = 0.00024) and social media time (adjusted mean difference −0.54 h, 95% CI −0.74 to −0.36, p = 0.00018) during school time, but there was no evidence for differences when comparing usage time on weekdays or weekends.