Xrail84 - ESRI:104050

WKT

GEOGCS["GCS_Xrail84", 
	DATUM["D_Xrail84", 
		SPHEROID["WGS_1984", 6378137.0, 298.257223563]], 
	PRIMEM["Greenwich", 0.0], 
	UNIT["Degree", 0.0174532925199433]]

WKT2

GEOGCRS["GCS_Xrail84", 
	DATUM["D_Xrail84", 
		ELLIPSOID["WGS_1984", 6378137.0, 298.257223563]], 
	PRIMEM["Greenwich", 0.0], 
	CS[ellipsoidal, 2], 
	AXIS["Longitude (lon)", east, 
		ORDER[1]], 
	AXIS["Latitude (lat)", north, 
		ORDER[2]], 
	ANGLEUNIT["Degree", 0.0174532925199433], 
	ID["Esri", "104050"]]

Data from @esri/proj-codes

{
  "wkid": 104050,
  "latestWkid": 104050,
  "macro": "PE_GCS_XRAIL84",
  "name": "GCS_Xrail84",
  "wkt": "GEOGCS[\"GCS_Xrail84\",DATUM[\"D_Xrail84\",SPHEROID[\"WGS_1984\",6378137.0,298.257223563]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.0174532925199433]]",
  "wkt2": "GEOGCRS[\"GCS_Xrail84\",DATUM[\"D_Xrail84\",ELLIPSOID[\"WGS_1984\",6378137.0,298.257223563]],PRIMEM[\"Greenwich\",0.0],CS[ellipsoidal,2],AXIS[\"Longitude (lon)\",east,ORDER[1]],AXIS[\"Latitude (lat)\",north,ORDER[2]],ANGLEUNIT[\"Degree\",0.0174532925199433],ID[\"Esri\",\"104050\"]]",
  "description": "Xrail84",
  "authority": "Esri",
  "version": "10.4.0",
  "deprecated": "no",
  "areaname": "UK - London",
  "extent": {
    "slat": 51.2,
    "nlat": 51.8,
    "llon": -0.7,
    "rlon": 0.6
  }
}