Hi all, I just finish the GAMER frontend for YT, and below I want to summarize some issues and things that might be confusing in the current skeleton frontend. I appreciate if you could help validate these issues and/or clarify some points in the section "Things to be clarified". Hopefully it will make frontend implementation easier in the future. I'll collect all comments and issue a PR for the revised skeleton. It will be complementary to the recent PR #2130 by Jonah Miller, which provides an extremely helpful example frontend. *Things to be clarified:*============================ 1. Difference between *FieldInfoContainer.known_other_fields* and *GridIndex._detect_output_field*: => known_other_fields contains fields that *might* be in an output, and lists their units and aliases. _detect_output_fields finds the fields that are defined in the currently loaded dataset. 2. *Dataset.unique_identifier*: => ?? 3. Set *AMRGridPatch.Parent = None* for grids without parents, and *AMRGridPatch.Children = []* for grids without children 4. Field array returned by *BaseIOHandler._read_fluid_selection* should be contiguous along the z instead of x direction. Therefore, for C-like array with the dimension [x][y][z] and for Fortran-like array with the the dimension (z,y,x), a matrix transpose is required (e.g., using np_array.transpose() or np_array.swapaxes(0,2)) 5. *start_index, stop_index, *and *ActiveDimension*s in the AMRGridPatch objects => ?? (1) It looks like stop_index is not used anymore (2) ActiveDimensions will be set by AMRGridPatch._prepare_grid. So perhaps frontend does not need to set it explicitly anymore (3) It seems that start_index is also calculated automatically 6. *chunk, selector, *and *_read_chunk_data* in io.py. => ?? Also the following comment about caching is confusing: def _read_chunk_data(self, chunk, fields): # This reads the data from a single chunk, and is only used for caching. 7. float type: (1) *GridIndex.float_type* is the float type for left and right simulation edges and must be float64 now (2) *BaseIOHandler._read_fluid_selection* should always return float64 now even if the on-disk data are stored in single precision 8. Difference between *add_output_field *and *add_field *used in FieldInfoContainer.setup_fluid_fields: 9. Dataset._parse_parameter_file: what does the following comment mean "Note that these are all assumed to be in code units; domain_left_edge and domain_right_edge will be updated to be in code units at a later time" => Perhaps it means that "domain_left_edge and domain_right_edge will be converted to YTArray automatically at a later time"? *Missing procedure*============================ 1. Add the new frontend in *frontends/api.py* 2. Set *GridIndex.max_level* 3. Set *Dataset.refine_by* *Bugin the current skeleton frontend* ============================ 1. data_structures.py: *self.dataset* is not set in GridIndex.__init__ when calling self.index_filename = self.dataset.parameter_filename 2. data_structures.py: replace self.Parent=[] by *self.Parent = None* 3. fields.py: the *field_list *argument is missing in FieldInfoContainer.__init__. This issue has been fixed in Jonah's PR. def __init__(self, ds, field_list): super(SkeletonFieldInfo, self).__init__(ds, field_list) Sincerely, Hsi-Yu (Justin)