When I said "all good" re my font, I was talking in terms of it actually compiling.

Glyph substitution, however, is another matter.

I had a sample word ending in the letters "NATION".

When I view the OT representation of the word, the "AT" [A_T] glyph substitution is picked up, instead of what I want, which is the T_I_O_N glyph.

Here are the contents of the substitution . . .

feature liga { # Standard Ligatures

# Latin

sub A T A by A_T_A;

sub A T E by A_T_E;

sub A T H by A_T_H;

sub A T R by A_T_R;

sub A A by A_A;

sub A C by A_C;

sub A D by A_D;

sub A E by A_E;

sub A F by A_F;

sub A G by A_G;

sub A H by A_H;

sub A I by A_I;

sub A K by A_K;

sub A N by A_N;

sub A O by A_O;

sub A R by A_R;

sub A S by A_S;

sub A T by A_T;

sub A U by A_U;

sub A V by A_V;

sub A W by A_W;

sub A X by A_X;

sub A Y by A_Y;

sub A Z by A_Z;

sub C A by C_A;

sub C C by C_C;

sub C D by C_D;

sub C E by C_E;

sub C F by C_F;

sub C G by C_G;

sub C H by C_H;

sub C I by C_I;

sub C K by C_K;

sub C L by C_L;

sub C M by C_M;

sub C N by C_N;

sub C O by C_O;

sub C R by C_R;

sub C S by C_S;

sub C T by C_T;

sub C U by C_U;

sub C V by C_V;

sub C W by C_W;

sub C X by C_X;

sub C Y by C_Y;

sub C Z by C_Z;

sub E T A by E_T_E;

sub E T H by E_T_H;

sub E T R by E_T_R;

sub E A by E_A;

sub E C by E_C;

sub E D by E_D;

sub E E by E_E;

sub E F by E_F;

sub E G by E_G;

sub E H by E_H;

sub E I by E_I;

sub E K by E_K;

sub E L by E_L;

sub E N by E_N;

sub E O by E_O;

sub E R by E_R;

sub E S by E_S;

sub E T by E_T;

sub E U by E_U;

sub E V by E_V;

sub E W by E_W;

sub E X by E_X;

sub E Y by E_Y;

sub E Z by E_Z;

sub F A by F_A;

sub F C by F_C;

sub F D by F_D;

sub F E by F_E;

sub F F by F_F;

sub F G by F_G;

sub F H by F_H;

sub F I by F_I;

sub F K by F_K;

sub F L by F_L;

sub F N by F_N;

sub F O by F_O;

sub F R by F_R;

sub F S by F_S;

sub F T by F_T;

sub F U by F_U;

sub F V by F_V;

sub F W by F_W;

sub F X by F_X;

sub F Y by F_Y;

sub F Z by F_Z;

sub G H T by G_H_T;

sub G T H by G_T_H;

sub I T A by I_T_A;

sub I T E by I_T_E;

sub I T H by I_T_H;

sub I T R by I_T_R;

sub I T Y by I_T_Y;

sub K A by K_A;

sub K C by K_C;

sub K D by K_D;

sub K E by K_E;

sub K F by K_F;

sub K G by K_G;

sub K H by K_H;

sub K I by K_I;

sub K K by K_K;

sub K L by K_L;

sub K N by K_N;

sub K O by K_O;

sub K R by K_R;

sub K S by K_S;

sub K T by K_T;

sub K U by K_U;

sub K V by K_V;

sub K W by K_W;

sub K X by K_X;

sub K Y by K_Y;

sub K Z by K_Z;

sub L T H by L_T_H;

sub L A by L_A;

sub L C by L_C;

sub L D by L_D;

sub L E by L_E;

sub L F by L_F;

sub L G by L_G;

sub L H by L_H;

sub L I by L_I;

sub L K by L_K;

sub L L by L_L;

sub L N by L_N;

sub L O by L_O;

sub L R by L_R;

sub L S by L_S;

sub L T by L_T;

sub L U by L_U;

sub L V by L_V;

sub L W by L_W;

sub L X by L_X;

sub L Y by L_Y;

sub L Z by L_Z;

sub O T A by O_T_A;

sub O T E by O_T_E;

sub O T H by O_T_H;

sub O T R by O_T_R;

sub R T A by R_T_A;

sub R T E by R_T_E;

sub R T R by R_T_R;

sub R A by R_A;

sub R C by R_C;

sub R D by R_D;

sub R E by R_E;

sub R F by R_F;

sub R G by R_G;

sub R H by R_H;

sub R I by R_I;

sub R K by R_K;

sub R N by R_N;

sub R O by R_O;

sub R R by R_R;

sub R S by R_S;

sub R T by R_T;

sub R U by R_U;

sub R V by R_V;

sub R W by R_W;

sub R X by R_X;

sub R Y by R_Y;

sub R Z by R_Z;

sub S T A by S_T_A;

sub S T E by S_T_E;

sub S T H by S_T_H;

sub S T I by S_T_I;

sub S T O by S_T_O;

sub S T R by S_T_R;

sub S T U by S_T_U;

sub S T Y by S_T_Y;

sub T A by T_A;

sub T C by T_C;

sub T D by T_D;

sub T E by T_E;

sub T F by T_F;

sub T G by T_G;

sub T H by T_H;

sub T I by T_I;

sub T K by T_K;

sub T N by T_N;

sub T O by T_O;

sub T R by T_R;

sub T S by T_S;

sub T T by T_T;

sub T U by T_U;

sub T V by T_V;

sub T W by T_W;

sub T X by T_X;

sub T Y by T_Y;

sub T Z by T_Z;

sub U T A by U_T_A;

sub U T E by U_T_E;

sub U T H by U_T_H;

sub U T R by U_T_R;

sub Y T H by Y_T_H;

sub T I O N by T_I_O_N;

sub S I O N by S_I_O_N;

} liga;

I have tried placing "sub T I O N by T_I_O_N;" as the first statement instead of one of the last, but it makes no difference.

*NB* have also tried this with latest 5.2 build and get the same results