The periodical has 'rigid' [='strict', 'inflexible'] guidelines for submissions.
a 'rigid' [='strict, unwavering'] adherence to the rules
The soldiers stood 'rigidly' at attention.
(..) But as you well know, sometimes one must break the rules in order to serve the greater good. Mordo won't see it that way. Mordo's soul is rigid and unmovable, forged by the fires of his youth. He needs your flexibility, just as you need his strength. Only together, do you stand a (..)2016 Doctor Strange