content: type = "object"
  required = ["attributes"]
  title = "Iteration"
  description = "One iteration/snapshot."
  
  [properties]
  
  #################
  # Particle data #
  #################
  
  [properties.particles]
  type = "object"
  title = "Particles"
  description = "Dict of particle species types."
  
  [properties.particles.properties.attributes]
  title = "Attribute layout"
  description = "Custom attributes allowed, no required attributes defined."
  "$ref" = "attributes.json"
  
  #####################################
  # Particle data -> Particle Species #
  #####################################
  
  [properties.particles.patternProperties."^(?!attributes).*"]
  title = "Particle Species"
  "$ref" = "particle_species.json"
  
  #############
  # Mesh data #
  #############
  
  [properties.meshes]
  type = "object"
  title = "Meshes"
  description = "Dict of meshes."
  
  [properties.meshes.properties.attributes]
  title = "Attribute layout"
  description = "Custom attributes allowed, no required attributes defined."
  "$ref" = "attributes.json"
  
  
  ###########################
  # Mesh data -> Mesh types #
  ###########################
  
  [properties.meshes.patternProperties."^(?!attributes).*"]
  title = "Mesh"
  "$ref" = "mesh.json"
  
  ########################
  # Iteration attributes #
  ########################
  
  
  [properties.attributes]
  title = "Attributes"
  
  # First requirement: standard-defined attributes
  
  [[properties.attributes.allOf]]
  required = ["dt", "time", "timeUnitSI"]
  title = "Iteration attributes"
  description = "Standard-defined attributes at the Iteration level."
  
  [properties.attributes.allOf.properties]
  timeUnitSI."$ref" = "attribute_defs.json#/$defs/float_attribute"
  time."$ref"       = "attribute_defs.json#/$defs/float_attribute"
  dt."$ref"         = "attribute_defs.json#/$defs/float_attribute"
  
  # Second condition: General layout of attributes
  
  [[properties.attributes.allOf]]
  title = "Attribute layout"
  "$ref" = "attributes.json"
  