Applying a Little Artificial Intelligence to a Patched Titlecaps Algorithm

Question

This question is based on @StevenB.Segletes' patch for titlecaps found here: Reformatting a Paragraph Consisting Entirely of Capital Letters

Consider the code:

\documentclass[12pt]{article}
\usepackage{titlecaps,xpatch}
\usepackage{newpxtext} % for bold small caps
\def\explowerchar#1{%
  \ifcase\numexpr`#1-`A\relax
   a\or b\or c\or d\or e\or f\or g\or h\or i\or j\or k\or l\or m\or
   n\or o\or p\or q\or r\or s\or t\or u\or v\or w\or x\or y\or z\else
   #1\fi
}
\makeatletter
\xpatchcmd{\title@string}{\@thestring#2}{\@thestring\explowerchar{#2}}{}{}
\makeatother

\begin{document}
\thispagestyle{empty}

This is a paragraph in which the first letter of each word is lower case beginning with the second word of each sentence. Applying the algorithm, the same paragraph is produced with every word capitalized.

\vspace{15pt}

\noindent \textbf{\scshape{After Applying the Algorithm:}}

\vspace{10pt}

\titlecap{This is a paragraph in which the first letter of each word is lower case beginning with the second word of each sentence. Applying the algorithm, the same paragraph is produced with every word capitalized.}
\end{document}

which produces

QUESTION: How may the patched algorithm be modified in order to prevent capitalization of words such as "is," "a," "on," "the," "of," "with" that are not the first word of a sentence?

Thank you.

Answer 1

You could use the mfirstuc package and add a list of excluded words yourself or use the mfirstuc-english package which already comes with several excluded words:

\documentclass[12pt]{article}

\usepackage{mfirstuc-english}
\MFUnocap{is}

\begin{document}

\capitalisewords{This is a paragraph in which the first letter of each word is lower case beginning with the second word of each sentence. Applying the algorithm, the same paragraph is produced with every word capitalized.}

\end{document}

Answer 2

No packages.

\documentclass[12pt]{article}
\usepackage{newpxtext} % for bold small caps

\linespread{1.04} % Palatino is quite high

\ExplSyntaxOn

\NewDocumentCommand{\titlecap}{m}
 {
  \dds_caps:e { \text_expand:n {#1} }
 }

\clist_const:Nn \c_dds_caps_lc_clist
 {
  a, an, and, but, for, in, of, or, no,
  nor, so, some, the, with, yet,
  is, % <--- sure?
  ís, % <--- just for example
 }
\seq_new:N \l__dds_caps_text_in_seq
\seq_new:N \l__dds_caps_text_out_seq

\cs_new_protected:Nn \dds_caps:n
 {
  \seq_set_split:Nnn \l__dds_caps_text_seq {~} {#1}
  \seq_clear:N \l__dds_caps_text_out_seq
  \seq_map_inline:Nn \l__dds_caps_text_seq
   {
    \clist_if_in:NnTF \c_dds_caps_lc_clist {##1}
     {% exception
      \seq_put_right:Nn \l__dds_caps_text_out_seq {##1}
     }
     {% capitalize
      \seq_put_right:Ne \l__dds_caps_text_out_seq { \text_titlecase_first:n {##1} }
     }
   }
   \seq_use:Nn \l__dds_caps_text_out_seq {~}
 }
\cs_generate_variant:Nn \dds_caps:n {e}

\ExplSyntaxOff

\begin{document}
\thispagestyle{empty}

This is a paragraph in which the first letter of each word 
is lower case beginning with the second word of each sentence. 
Applying the algorithm, the same paragraph is produced with 
every word capitalized.

\vspace{15pt}

\noindent \textbf{\scshape{After Applying the Algorithm:}}

\vspace{10pt}

\titlecap{
  This is a paragraph in which the first letter of each ŵord 
  ís lower case beginning with the second word of each sentence. 
  Applying the àlgorithm, the same paragraph is produced with 
  every word čapitalized.
}

\end{document}

The text is split at spaces, then each word is processed and capitalized unless it's in the list of exceptions; the processed word is put in another sequence that's delivered with a space between items.

Note that words followed by punctuation will not be recognized as an exception, which in my opinion is correct.

I added some accented characters just to show that they're treated correctly.

Answer 3

This also suits with your requirement:

\documentclass{book}
\usepackage{titlecaps}%

\begin{document}

\Addlcwords{is the of that for in and a with in}%%add what ever you like

\titlecap{This is for test The}

\end{document}