detailed rule book. because ultimately, border controls and travel policy depend on individual member states. and what that means is that check the rules that apply to your specific european destination, because even though the eu says it wants to harmonize travel policy, requirements vary. for instance, holidaying on the french river ra for americans is already possible. the tourists who can show proof of vaccination plus a negative covid test. where as in greece, unvaccinated americans can go island hopping. all they need to show is the negative test. and a word of caution. these rules can change on a dime. european borders can be shut quickly depending on the pandemic, especially on the emergence of possible variants of concern. cyril varnier, cnn, london. so for more on this, let s bring in simon color, the travel editor from the independent and joining me via skype from bath,