W3C validation tests complain if a file includes any characters with ASCII decimal values 128 through 159. Presence of these characters does not preclude validation. However, if the file contains real validation errors, the W3C validator reports these characters along with the actual errors. If you fix the errors, and leave the characters, the complaint becomes just a note about “non-SGML” characters.
Note: Leaving these characters in your document does not make the output invalid, despite the somewhat misleading way the W3C validator lists them when something else in the output is not valid.
For most purposes you should not need to do anything about the characters in question. However, if you want to have DITA2Go remap or remove the offending characters, you can set the following option:
[HTMLOptions] ; ValidOnly = No (default, allow normal use of chars from 128 to 160), ; or Yes (for warning-free W3C validation, remaps or removes ; those chars) ValidOnly=Yes
This option affects the following characters:
Setting ValidOnly=Yes changes the output as follows:
Table 22-3 shows how DITA2Go treats characters in this range when ValidOnly=Yes. Depending on which version of the DITA2Go User’s Guide you are using to view the table, some characters might not be displayed.
§22.4.3 Specifying character encoding for HTML