Fix multiple validation errors for EMG coordsystem and electrode files

src/schema/rules/errors.yaml

@@ -142,8 +142,8 @@ SidecarWithoutDatafile:
   level: error
   selectors:
     - extension == ".json"
-    - suffix != "coordsystem" || modality != "emg"
-    # ↑ EMG allows multiple coordsys files per data file (distinguished via `space` entity)
+    - suffix != "coordsystem"
+    # ↑ coordsystem files can be shared via inheritance principle and may not have direct data files
 
 # BIDS Validator Original Issue Code #97
 MissingSession:

src/schema/rules/files/raw/channels.yaml

@@ -62,12 +62,29 @@ coordsystem__eeg:
     space: optional
 
 # emg may have a `recording` entity
+# EMG coordsystem files can be at root level (no subject) when using
+# the inheritance principle for shared coordinate systems across subjects
 coordsystem__emg:
   $ref: rules.files.raw.channels.coordsystem__eeg
   datatypes:
     - emg
   entities:
     $ref: rules.files.raw.channels.coordsystem__eeg.entities
+    subject: optional
+    recording: optional
+    space: optional
+
+# EMG coordsystem files at dataset root level (no datatype directory)
+# Used for sharing coordinate systems across all subjects via inheritance
+# Example: /space-leftForearm_coordsystem.json
+coordsystem__emg_root:
+  suffixes:
+    - coordsystem
+  extensions:
+    - .json
+  datatypes: []
+  entities:
+    session: optional
     recording: optional
     space: optional
 

src/schema/rules/tabular_data/emg.yaml

@@ -29,17 +29,41 @@ EMGChannels:
   index_columns: [name__channels]
   additional_columns: allowed_if_defined
 
+# EMG electrodes without group column - name must be unique
 EMGElectrodes:
   selectors:
     - datatype == "emg"
     - suffix == "electrodes"
     - extension == ".tsv"
+    - '!columns.group'
+  initial_columns:
+    - name__electrodes
+    - x
+    - y
+  columns:
+    name__electrodes: required
+    x: required
+    y: required
+    z: optional
+    coordinate_system: recommended
+    type__electrodes: recommended
+    material: recommended
+    impedance: recommended
+    group__emg: recommended
+  index_columns: [name__electrodes]
+  additional_columns: allowed_if_defined
+
+# EMG electrodes with group column - (name, group) must be unique
+EMGElectrodes__grouped:
+  selectors:
+    - datatype == "emg"
+    - suffix == "electrodes"
+    - extension == ".tsv"
+    - columns.group
   initial_columns:
     - name__electrodes
     - x
     - y
-    - z
-    - coordinate_system
   columns:
     name__electrodes: required
     x: required

tools/schemacode/src/bidsschematools/tests/test_render_text.py

@@ -118,6 +118,9 @@ def test_make_filename_template(schema_obj, schema_dir, placeholders):
             continue
         if line.startswith("    [ses-<label>/]"):
             continue
+        # Skip patterns with optional subject (EMG coordsystem allows root-level placement)
+        if line.lstrip().startswith("[sub-<label>]"):
+            continue
 
         if line in datatype_bases:
             datatype_bases_found += 1
@@ -154,6 +157,9 @@ def test_make_filename_template(schema_obj, schema_dir, placeholders):
             continue
         if line.startswith("    [ses-<label>/]"):
             continue
+        # Skip patterns with optional subject (EMG coordsystem allows root-level placement)
+        if line.lstrip().startswith("[sub-<label>]"):
+            continue
 
         if line in datatype_bases:
             datatype_bases_found += 1