== relaxed binding matrix ==
canonical property: demo.relaxed.api-key

SPELLING                 SOURCE BINDER   ${} plain  ${} boot  
--------------------------------------------------------------
demo.relaxed.api-key     map    bound    bound      bound     
demo.relaxed.apiKey      map    bound    MISS       bound     
demo.relaxed.api_key     map    bound    MISS       bound     
demo.relaxed.APIKEY      map    bound    MISS       bound     
DEMO.RELAXED.API-KEY     map    bound    MISS       bound     
demo.relaxed.apikey      map    bound    MISS       bound     
demo.relaxed.api.key     map    MISS     MISS       MISS      
DEMO_RELAXED_API_KEY     env    bound    bound      bound     
DEMO_RELAXED_APIKEY      env    bound    MISS       bound     
demo_relaxed_api_key     env    bound    bound      bound     
DEMO.RELAXED.API-KEY     env    bound    bound      bound     

BINDER    = what @ConfigurationProperties sees (Binder)
${} plain = placeholder resolution against a bare StandardEnvironment
${} boot  = the same, after ConfigurationPropertySources.attach(env),
            which Spring Boot performs on every environment it prepares
bound     = the value arrived;  MISS = the property was not found