/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/ is in libgtksourceviewmm-3.0-dev 3.18.0-3.
This file is owned by root:root, with mode 0o755.
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/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/buffer_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/completion_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/completionactivation_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/completioncontext_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/completioninfo_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/completionitem_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/completionproposal_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/completionprovider_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/completionwords_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/gutter_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/gutterrenderer_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/gutterrendererpixbuf_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/gutterrenderertext_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/language_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/languagemanager_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/mark_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/markattributes_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/printcompositor_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/style_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/stylescheme_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/styleschememanager_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/undomanager_p.h
/usr/include/gtksourceviewmm-3.0/gtksourceviewmm/private/view_p.h