DOC: add section on LPA/RPA/..., consolidate links

src/99-appendices/08-coordinate-systems.md

@@ -84,7 +84,25 @@ option to specify the value as follows:
 of restricted keywords for MEG, EEG, or iEEG, please open a new issue on the
 [bids-standard/bids-specification GitHub repository](https://github.com/bids-standard/bids-specification/issues/new/choose).**
 
-## MEG Specific Coordinate Systems
+Note that the short descriptions below may not capture all details.
+For detailed descriptions of the coordinate systems below, please see the
+[FieldTrip webpage](https://www.fieldtriptoolbox.org/faq/how_are_the_different_head_and_mri_coordinate_systems_defined).
+
+### Commonly used anatomical landmarks in MEG, EEG, and iEEG research
+
+In the documentation below we refer to anatomical landmarks such as the
+Left Pre Auricular point (LPA) and the Right Pre Auricular point (RPA),
+or the left and right Helix-Tragus Junction (LHJ, RHJ).
+
+These anatomical landmarks are commonly used in MEG, EEG, and iEEG research
+to define coordinate systems that capture digitized sensor positions.
+
+More information can be obtained from the FieldTrip webpage.
+
+- [FAQ: LPA and RPA](https://www.fieldtriptoolbox.org/faq/how_are_the_lpa_and_rpa_points_defined/)
+- [FAQ: Beyond LPA and RPA](https://www.fieldtriptoolbox.org/faq/how_should_i_report_the_positions_of_the_fiducial_points_on_the_head/)
+
+### MEG Specific Coordinate Systems
 
 Restricted keywords for the `<CoordSysType>CoordinateSystem` field in the
 `coordinatesystem.json` file for MEG datasets:
@@ -105,11 +123,7 @@ can also be applied to MEG:
 -   `EEGLAB`
 -   `EEGLAB-HJ`
 
-Note that the short descriptions above do not capture all details, there are
-detailed extensive descriptions of these coordinate systems on the
-[FieldTrip toolbox web page](https://www.fieldtriptoolbox.org/faq/how_are_the_different_head_and_mri_coordinate_systems_defined)
-
-## EEG Specific Coordinate Systems
+### EEG Specific Coordinate Systems
 
 Restricted keywords for the `<CoordSysType>CoordinateSystem` field in the
 `coordsystem.json` file for EEG datasets:
@@ -137,11 +151,7 @@ can also be applied to EEG:
 -   `KitYokogawa`
 -   `ChietiItab`
 
-Note that the short descriptions above do not capture all details, There are
-detailed extensive descriptions of these coordinate systems on the
-[FieldTrip toolbox web page](https://www.fieldtriptoolbox.org/faq/how_are_the_different_head_and_mri_coordinate_systems_defined).
-
-## iEEG Specific Coordinate Systems
+### iEEG Specific Coordinate Systems
 
 Restricted keywords for the `<CoordSysType>CoordinateSystem` field in the
 `coordsystem.json` file for iEEG datasets: