How to search for a phrase that includes a comma using xesearch?

Question

I am using xelatex and trying to italicize a text segment that includes a comma. The only way ahead that I know of is by using xesearch and its command SearchList. It works for the most part, but if the phrase includes a comma I simply can't seem to pass the entire phrase as a single argument to the command (by escaping the comma). Here is an example of what I am trying to do:

\documentclass[11pt, a4paper]{article}
\usepackage{xesearch}
\begin{document}
  a, b, abc, b, a, b, c

  \SearchList*{list1}{\textit{#1}}{a, b}

  a, b, abc, b, a, b, c

  \StopList{list1}
\end{document} 

Doing this matches the a's but does not italicize the b's anywhere. The culprit seems to be the space in front of the b that is passed as an argument to SearchList. Removing the space so that the line now reads

\SearchList*{list1}{\textit{#1}}{a,b}

results in the single a and b's being italicized (as expected).

However, I am specifically trying to italicize the segment "a, b" (with a comma and a space between the letters), ignoring other instances of the letter b. All the occurrences of "a, b" -- two in this case -- should be italicized.

I have tried adding braces following the advice found here: how do I escape a comma? although I must admit that I don't fully understand escape sequences in latex. This is what I have tried:

\documentclass[11pt, a4paper]{article}
\usepackage{xesearch}
\begin{document}
a, b, abc, b, a, b, c

\UndoBoundary{,}
\SearchList*{list1}{\textit{#1}}{{a, b}}

a, b, abc, b, a, b, c

\StopList{list1}
\MakeBoundary{,}
\end{document}

This seems to not do anything. Any help would be appreciated.

Answer 1

I don't know the xesearch package but you could use expl3 regex:

\documentclass[11pt, a4paper]{article}
\usepackage{expl3}

\ExplSyntaxOn
\cs_new_protected:Npn \zz #1
 {
  \tl_set:Nn \l_tmpa_tl { #1 }
  \regex_replace_all:nnN {a,\s b}{\c{textit}\cB\{\0\cE\}} \l_tmpa_tl
  \tl_use:N \l_tmpa_tl
 }
\ExplSyntaxOff

\begin{document}

a, b, abc, b, a, b, c

\zz{a, b, abc, b, a, b, c}

\end{document}

Answer 2

A listofitems approach.

\documentclass[11pt, a4paper]{article}
\usepackage{listofitems}
\begin{document}
a, b, abc, b, a, b, c

\setsepchar{a, b}
\readlist\mylist{a, b, abc, b, a, b, c}
\foreachitem\i\in\mylist{\ifnum\icnt>1\relax\textit{\mylistsep[\icnt]}\fi\i}
\end{document} 

In macro form, it could be done as such:

\documentclass[11pt, a4paper]{article}
\usepackage{listofitems}
\newcommand\mysearch[2][a, b]{%
  \setsepchar{#1}%
  \readlist\mylist{#2}%
  \foreachitem\i\in\mylist{\ifnum\icnt>1\relax\textit{\mylistsep[\icnt]}\fi\i}%
}
\begin{document}
a, b, abc, b, a, b, c

\mysearch{a, b, abc, b, a, b, c}

\mysearch[abc, b]{a, b, abc, b, a, b, c}
\end{document}