expr: docu update.

doc/tex/mod/Exprf

@@ -184,6 +184,11 @@ STRING  File with processing instructions
 @EndParameter
 
 
+@BeginNote
+The expr commands sellevel(x,k) and sellevidx(x,k) are only avaiable with @oper{exprf}/@oper{aexprf}.
+@EndNote
+
+
 @BeginExample
 Assume an input dataset contains at least the variables 'aprl', 'aprc' and 'ts'.
 To create a new variable 'var1' with the sum of 'aprl' and 'aprc' and a variable 'var2'

src/operator_help.h

@@ -1264,7 +1264,7 @@ static const char *EnlargeHelp[] = {
     "    enlarge,grid  ifile ofile",
     "",
     "DESCRIPTION",
-    "    Enlarge all fields of ifile to a user given grid. Normally only the last ",
+    "    Enlarge all fields of ifile to a user given horizontal grid. Normally only the last ",
     "    field element is used for the enlargement. If however the input and output",
     "    grid are regular lon/lat grids, a zonal or meridional enlargement is possible.",
     "    Zonal enlargement takes place, if the xsize of the input field is 1 and ",
@@ -1436,6 +1436,9 @@ static const char *ExprHelp[] = {
     "PARAMETER",
     "    instr     STRING  Processing instructions (need to be 'quoted' in most cases)",
     "    filename  STRING  File with processing instructions",
+    "",
+    "NOTE",
+    "    The expr commands sellevel(x,k) and sellevidx(x,k) are only avaiable with exprf/aexprf.",
     NULL
 };