Fontspec help, combining fonts

Question

I am struggling with font selection. I just cant seem to get a grasp on this.

I have a document class I'm developing which uses Latin Modern Roman, Trajan Pro, and Trajan Pro Bold. My needs are to define the Trajan fonts to small caps and bold small caps while using LRM for everything else.

I cannot figure out why the following [options] causes an error, or how to get around it.

\documentclass[11pt]{article}

\usepackage{geometry}           %for page layout
\geometry{hmargin={1in,1in},vmargin={0.75in,0.75in},marginparwidth={0.8in},marginparsep={0in}}

\usepackage{fontspec}   %for xelatex unicode
    \setmainfont{Latin Modern Roman}[
        UprightFeatures = {SmallCapsFont=TrajanPro-Regular.otf},
        BoldFeatures = {SmallCapsFont=TrajanPro-Bold.otf},
    ]

\begin{document}

Here is some {\bfseries\scshape Boldface SmallCaps} text

Here is some {\bfseries\uppercase{Boldface Uppercase}} text

Here is some {\bfseries Boldface} text

Here is some {\scshape SmallCaps} text

Here is some \uppercase{Uppercase} text

Here is some {Regular} text

\end{document}

As an edit, I have added the following work around code I have been using for almost 5 years. This works just fine. everywhere I would want to type \scshape I just have typed \sffamily instead. I know its wrong to do so but in over 5 years of trying to figure out a better way I never have.

\RequirePackage{fontspec}           %for xelatex unicode
    \setmainfont{Latin Modern Roman}
%        BoldFont = ⟨font name⟩ 
%        ItalicFont = ⟨font name⟩ 
%        BoldItalicFont = ⟨font name⟩ 
%        SlantedFont = ⟨font name⟩ 
%        BoldSlantedFont = ⟨font name⟩ 
%        SmallCapsFont = ⟨font name⟩


    \setsansfont{TrajanPro-Regular.otf}[
        BoldFont=TrajanPro-Bold.otf
%        ItalicFont = ⟨font name⟩ 
%        BoldItalicFont = ⟨font name⟩ 
%        SlantedFont = ⟨font name⟩ 
%        BoldSlantedFont = ⟨font name⟩ 
%        SmallCapsFont = ⟨font name⟩
    ]

As one more edit, LRM is a system installed font, the Trajan fonts are two files I keep with my projects in the root directory. I would like to be able to put them into a font folder inside the root, but one step at a time.

Answer 1

I haven't got Trajan-Pro, so I have substituted something else that will be obviously different than LMR (TexGyreHeros).

\documentclass[11pt]{article}

\usepackage{geometry}           %for page layout
\geometry{hmargin={1in,1in},vmargin={0.75in,0.75in},marginparwidth={0.8in},marginparsep={0in}}

\usepackage{fontspec}  %% running under LuaLaTeX

\setmainfont{Latin Modern Roman}[
        SmallCapsFeatures={Letters=SmallCaps}, % <=== See Section 4.1 of Fontspec documentation.  
        UprightFeatures = {SmallCapsFont=texgyreheros-regular.otf},
        BoldFeatures = {SmallCapsFont=texgyreheros-bold.otf},
    ]


\begin{document}
Here is some {\bfseries\scshape Boldface SmallCaps} text

Here is some {\bfseries\uppercase{Boldface Uppercase}} text

Here is some {\bfseries Boldface} text

Here is some {\scshape SmallCaps} text

Here is some \uppercase{Uppercase} text

Here is some {Regular} text
\end{document}

The one change made is to add the line SmallCapsFeatures={Letters=SmallCaps}, for the reasons discussed in the Fontspec documentation in Section 4.1.

This code works on my system under LuaLaTeX, but not XeLaTeX -- perhaps because I do not have LMR installed as a system font; for LuaLaTeX, LMR is the default font. To test that idea, the following code substitutes one of my system fonts for LMR (TeX Gyre Termes):

%% using the free Tex Gyre fonts, which I have installed as system fonts
\setmainfont{TeXGyreTermesX}[
     SmallCapsFeatures={Letters=SmallCaps}, % <=== See Section 4.1 of Fontspec documentation.  
     UprightFeatures = {SmallCapsFont=texgyreheros-regular.otf}, 
     BoldFeatures = {SmallCapsFont=texgyreheros-bold.otf},
    ]

With this change, I get the same result for either LuaLaTeX or XeLaTeX:

Two additional notes may be helpful. First, Will Robertson has recently recommended using explicit file names, rather than the "human-readable" system names TUGBoat 39 (2018). Second, the SmallCapsFeatures can be embedded into the the other features, so that you have additional control for upright or bold:

\setmainfont{texgyretermes}[
Extension = {.otf},
UprightFont = {*-regular}, 
ItalicFont = {*-italic},
BoldFont = {*-bold}, 
BoldItalicFont = {*-bolditalic},
UprightFeatures = {SmallCapsFont=texgyreheros-regular.otf, SmallCapsFeatures={Letters=SmallCaps, Color=992211}},
BoldFeatures    = {SmallCapsFont=/Users/John/Library/Fonts/FiraGO-Heavy.otf,   SmallCapsFeatures={Letters=SmallCaps, Color=112299}, Color = FF4422},
]

Your can give the full path to your Trajan-Pro font files, e.g., as I have done here for FiraGO-Heavy.