In 1.5.0 tag (major under 2.0.0) specified php>=5.5.5, but it depends on sabre/uri with version gap >=1.0,<3.0.0. sabre/uri version >2.0.0 depends on php>7. Thus, if i try install sabre/xml<2.0.0 with php < 7, it's fails with not satisfy requirement.
In 1.5.0 tag (major under 2.0.0) specified php>=5.5.5, but it depends on sabre/uri with version gap >=1.0,<3.0.0. sabre/uri version >2.0.0 depends on php>7. Thus, if i try install sabre/xml<2.0.0 with php < 7, it's fails with not satisfy requirement.