Install libgtkspellmm-3.0-doc by entering the following commands in the terminal:
sudo apt update sudo apt install libgtkspellmm-3.0-doc
Description:
C++ wrappers for GtkSpell (documentation)
GtkSpellmm provides C++ bindings for the GtkSpell spell-checking library. GtkSpell provides LibreOffice-style highlighting of misspelled words in a GtkTextView widget. Right-clicking a misspelled word pops up a menu of suggested replacements. . This package contains the HTML reference documentation.
Homepage: http://gtkspell.sourceforge.net
Version: 3.0.5+dfsg-1
Section: universe/doc