[troff]: Clarify diagnostic messages.

* src/roff/troff/div.cpp (top_level_diversion::output)
  (top_level_diversion::transparent_output)
  (top_level_diversion::copy_file): Clarify diagnostic messages.

They are lengthy--troff is not a simple machine, alas.

2 files changed, 14 insertions, 7 deletions

diff --git a/ChangeLog b/ChangeLog
index 437f38ef1..6c0fde1ce 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2024-01-08  G. Branden Robinson <g.branden.robinson@gmail.com>
 
+	* src/roff/troff/div.cpp (top_level_diversion::output)
+	(top_level_diversion::transparent_output)
+	(top_level_diversion::copy_file): Clarify diagnostic messages.
+
+2024-01-08  G. Branden Robinson <g.branden.robinson@gmail.com>
+
 	[troff]: Trivially refactor.
 
 	* src/roff/troff/div.cpp (top_level_diversion::begin_page):
diff --git a/src/roff/troff/div.cpp b/src/roff/troff/div.cpp
index 36cf11773..6ac9ef017 100644
--- a/src/roff/troff/div.cpp
+++ b/src/roff/troff/div.cpp
@@ -400,8 +400,9 @@ void top_level_diversion::output(node *nd, int retain_size,
   vunits next_trap_pos;
   trap *next_trap = find_next_trap(&next_trap_pos);
   if (before_first_page && begin_page())
-    fatal("attempting diversion output before first page has started;"
-	  " invoke break or flush request earlier");
+    fatal("attempting diversion output before first page has started,"
+	  " when a top-of-page trap is defined; invoke break or flush"
+	  " request beforehand");
   vertical_size v(vs, post_vs);
   for (node *tem = nd; tem != 0; tem = tem->next)
     tem->set_vertical_size(&v);
@@ -449,9 +450,9 @@ void top_level_diversion::output(node *nd, int retain_size,
 void top_level_diversion::transparent_output(unsigned char c)
 {
   if (before_first_page && begin_page())
-    fatal("attempting transparent output of top-level diversion before"
-	  " first page has started; invoke break or flush request"
-	  " earlier");
+    fatal("attempting transparent output from top-level diversion"
+	  " before first page has started, when a top-of-page trap is"
+	  " defined; invoke break or flush request beforehand");
   const char *s = asciify(c);
   while (*s)
     the_output->transparent_char(*s++);
@@ -470,8 +471,8 @@ void top_level_diversion::copy_file(const char *filename)
 {
   if (before_first_page && begin_page())
     fatal("attempting transparent copy of file to top-level diversion"
-	  " before first page has started; invoke break or flush"
-	  " request earlier");
+	  " before first page has started, when a top-of-page trap is"
+	  " defined; invoke break or flush request beforehand");
   the_output->copy_file(page_offset, vertical_position, filename);
 }