How to use sub contexts in Behat 3.0
The documentation is really poor indeed. AFAIK you don't have sub contexts, instead you now can define multiple contexts per suite.
# behat.ymldefault: suites: domain_features: paths: [ %paths.base%/features ] contexts: [ DomainContext ] web_features: paths: [ %paths.base%/features ] contexts: [ WebContext ] filters: tags: @web