/usr/share/doc/blt-dev/html/ is in blt-dev 2.5.3+dfsg-1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/doc/blt-dev/html/BLT.html
/usr/share/doc/blt-dev/html/Blt_Tree.html
/usr/share/doc/blt-dev/html/Blt_TreeCreate.html
/usr/share/doc/blt-dev/html/Blt_TreeCreateNode.html
/usr/share/doc/blt-dev/html/Blt_TreeDeleteNode.html
/usr/share/doc/blt-dev/html/Blt_TreeExists.html
/usr/share/doc/blt-dev/html/Blt_TreeGetNode.html
/usr/share/doc/blt-dev/html/Blt_TreeGetToken.html
/usr/share/doc/blt-dev/html/Blt_TreeName.html
/usr/share/doc/blt-dev/html/Blt_TreeNodeId.html
/usr/share/doc/blt-dev/html/Blt_TreeReleaseToken.html
/usr/share/doc/blt-dev/html/Blt_Vector.html
/usr/share/doc/blt-dev/html/barchart.html
/usr/share/doc/blt-dev/html/beep.html
/usr/share/doc/blt-dev/html/bgexec.html
/usr/share/doc/blt-dev/html/bitmap.html
/usr/share/doc/blt-dev/html/blt-index.html
/usr/share/doc/blt-dev/html/bltdebug.html
/usr/share/doc/blt-dev/html/busy.html
/usr/share/doc/blt-dev/html/container.html
/usr/share/doc/blt-dev/html/cutbuffer.html
/usr/share/doc/blt-dev/html/dragdrop.html
/usr/share/doc/blt-dev/html/eps.html
/usr/share/doc/blt-dev/html/graph.html
/usr/share/doc/blt-dev/html/hierbox.html
/usr/share/doc/blt-dev/html/hiertable.html
/usr/share/doc/blt-dev/html/htext.html
/usr/share/doc/blt-dev/html/spline.html
/usr/share/doc/blt-dev/html/stripchart.html
/usr/share/doc/blt-dev/html/table.html
/usr/share/doc/blt-dev/html/tabset.html
/usr/share/doc/blt-dev/html/tile.html
/usr/share/doc/blt-dev/html/tree.html
/usr/share/doc/blt-dev/html/treeview.html
/usr/share/doc/blt-dev/html/vector.html
/usr/share/doc/blt-dev/html/watch.html
/usr/share/doc/blt-dev/html/winop.html