diff --git a/text-crossrefs/text-crossrefs.lua b/text-crossrefs/text-crossrefs.lua
index 5960c2a..9d74255 100644
--- a/text-crossrefs/text-crossrefs.lua
+++ b/text-crossrefs/text-crossrefs.lua
@@ -15,6 +15,10 @@ local PLACE_LABEL_ATTR = 'refanchor'
 local IS_CONFIG_ARRAY = { ['additional_types'] = true }
 local RAW_ATTRIBUTE
 
+local function warning(message)
+  io.stderr:write('WARNING [text-crossrefs]: ' .. message .. '\n')
+end
+
 -- ConTeXt-specific tweak in order to add the label to the footnote
 --[[
   Placing the label in square brackets immediatly after \footnote
@@ -212,8 +216,8 @@ local function control_label_placement(span)
       span.content:insert(pandoc.Span({}, { id = id .. '-end' }))
       span.identifier = nil
     elseif label_placement ~= 'beg' then
-      error('Invalid value ' .. label_placement .. ' on attribute ' .. PLACE_LABEL_ATTR .. ': ' ..
-            'shoud be “beg” (default), “end” of “both”.')
+      warning('Invalid value ' .. label_placement .. ' on attribute ' .. PLACE_LABEL_ATTR .. ': ' ..
+           'shoud be “beg” (default), “end” of “both”. Using the defaults.')
     end
   end
   return span
@@ -237,14 +241,14 @@ local function labelize_span(span)
   end
 end
 
-local current_note_labels = {}
+local labels_in_current_note = {}
 
 local collect_note_labels = {
   Span = function(span)
     if span.identifier ~= ''
       and (config.only_explicit_labels == 'false' or span.classes:includes('label'))
     then
-      table.insert(current_note_labels, span.identifier)
+      table.insert(labels_in_current_note, span.identifier)
     end
   end
 }
@@ -257,14 +261,14 @@ local function make_notelabel(pos)
     if RAW_ATTRIBUTE == 'openxml' then
       raw_code = string.gsub(
         '<w:bookmarkStart w:id="{{label}}_Note" w:name="{{label}}_Note"/>',
-        '{{label}}', current_note_labels[1])
+        '{{label}}', labels_in_current_note[1])
     elseif RAW_ATTRIBUTE == 'context' then
-      raw_code = '\\withfirstopt[note:' .. current_note_labels[1] .. ']'
+      raw_code = '\\withfirstopt[note:' .. labels_in_current_note[1] .. ']'
     end
   elseif pos == 'end' then
     if RAW_ATTRIBUTE == 'openxml' then
       raw_code = string.gsub('<w:bookmarkEnd w:id="{{label}}_Note"/>',
-                             '{{label}}', current_note_labels[1])
+                             '{{label}}', labels_in_current_note[1])
     end
   end
   return pandoc.RawInline(RAW_ATTRIBUTE, raw_code)
@@ -277,18 +281,18 @@ local function labelize_note(note)
   return { label_begin, note, label_end }
 end
 
-local function map_text_to_note_labels(current_note_labels)
-  local note_label = 'note:' .. current_note_labels[1]
-  for _, text_label in ipairs(current_note_labels) do
-    text_to_note_labels[text_label] = note_label
+local function map_text_to_note_labels(labels_in_current_note)
+  local note_label = 'note:' .. labels_in_current_note[1]
+  for _, label in ipairs(labels_in_current_note) do
+    text_to_note_labels[label] = note_label
   end
 end
 
 function set_notelabels(note)
-  current_note_labels = {}
+  labels_in_current_note = {}
   pandoc.walk_inline(note, collect_note_labels)
-  if #current_note_labels > 0 then
-    map_text_to_note_labels(current_note_labels)
+  if #labels_in_current_note > 0 then
+    map_text_to_note_labels(labels_in_current_note)
     return labelize_note(note)
   end
 end
@@ -338,8 +342,8 @@ local function parse_next_reference(raw_references, beg_of_search)
   if beg_of_search < #raw_references then
     -- The delimiter can be composed of more than one character.
     local delim_beg, delim_end = string.find(raw_references,
-                                                                config.references_enum_separator,
-                                                                beg_of_search, true)
+                                             config.references_enum_separator,
+                                             beg_of_search, true)
     if delim_beg then
       reference = string.sub(raw_references, beg_of_search, delim_beg - 1)
       next_ref_beg = delim_end + 1
@@ -366,15 +370,17 @@ local function parse_references_enum(raw_references)
 end
 
 local function error_on_attr(attr_key, attr_value, span_content)
-  error('Invalid value "' .. attr_value .. '" for attribute "' .. attr_key ..
+  warning('Invalid value "' .. attr_value .. '" for attribute "' .. attr_key ..
           '" in the span with class "' .. TEXT_CROSSREF_CLASS ..
-          '" whose content is "' .. stringify(span_content) .. '".')
+          '" whose content is "' .. stringify(span_content) .. '". ' ..
+          'Using the defaults.')
 end
 
 local function get_ref_type(span)
   local ref_type = span.attributes[REF_TYPE_ATTR] or config.default_reftype
   if not accepted_types[ref_type] then
     error_on_attr(REF_TYPE_ATTR, ref_type, span.content)
+    ref_type = config.default_reftype
   end
   return ref_type
 end
@@ -383,6 +389,7 @@ local function if_prefixed(span)
   local prefixed_attr_value = span.attributes[PREFIXED_ATTR] or config.default_prefixref
   if prefixed_attr_value ~= 'yes' and prefixed_attr_value ~= 'no' then
     error_on_attr(PREFIXED_ATTR, prefixed_attr_value, span.content)
+    prefixed_attr_value = config.default_prefixref
   end
   local is_prefixed = true
   if prefixed_attr_value == 'no' then is_prefixed = false end
@@ -425,7 +432,12 @@ local function make_crossrefenum_references_list(refs, ref_type)
     if FORMAT == 'context'
       and (ref_type == 'note' or ref_type == 'pagenote')
     then
-      anchor = text_to_note_labels[anchor]
+      local note_label = text_to_note_labels[anchor]
+      if note_label then
+	anchor = note_label
+      else
+        warning('Wrong reference to non-existent label "' .. anchor .. '".')
+      end
     end
     local texified_ref = '{' .. anchor
     if ref.end_of_range then