Make a few comments more precise

v23/mkline.go

@@ -644,8 +644,9 @@ func (mkline *MkLine) ResolveExprsInRelPath(rel RelPath, pkg *Package) RelPath {
 
  if G.Testing {
  // Relative pkgsrc paths usually only contain two or three levels.
- // A possible reason for reaching this assertion is a pkglint unit test
- // that uses t.NewMkLines instead of the correct t.SetUpFileMkLines.
+ // If this assertion fails during a pkglint unit test,
+ // it is typically caused by calling t.NewMkLines
+ // instead of the correct t.SetUpFileMkLines.
  assertf(!pkgsrcdir.ContainsPath("../../../../.."),
  "Relative path %q for %q is too deep below the pkgsrc root %q.",
  pkgsrcdir, basedir, G.Pkgsrc.File("."))

v23/mkparser.go

@@ -436,9 +436,8 @@ func ToExpr(str string) *MkExpr {
 // MkCond is a condition in a makefile, such as ${OPSYS} == NetBSD.
 //
 // The representation is somewhere between syntactic and semantic.
-// Unnecessary parentheses are omitted in this representation,
-// (TODO: double-check; the 'paren(paren(paren()))' tests contradict)
-// but !empty(VARNAME) is represented differently from ${VARNAME} != "".
+// The condition '!empty(VARNAME)' is represented differently from the
+// condition '${VARNAME} != ""'.
 // For higher level analysis, a unified representation might be better.
 // See MkParser.MkCond.
 type MkCond struct {

v23/pkgsrc.go

@@ -943,7 +943,8 @@ func (src *Pkgsrc) Load(filename PkgsrcPath, options LoadOptions) *Lines {
 //
 // The relative path is built by going from the "from" directory up to the
 // pkgsrc root and from there to the "to" filename. This produces the form
-// "../../category/package" that is found in DEPENDS and .include lines.
+// "../../category/package" that is found in DEPENDS lines, as well as
+// .include lines from a package directory.
 //
 // This function should only be used if the relative path from one file to
 // another cannot be computed in another way. The preferred way is to take