Overfull \hbox from printindex

Question

I've got a index generated with makeindex but when compiling the file again, when the index is generated, I get a bunch of overfull \hbox.

This is an example of an index that results in overfull:

\begin{theindex}
  \item Type, 149, 155
    \subitem GetProperties(), 127, 130, 135, 150
\end{theindex}

I don't want to change the .ind-file manually, I'm guessing that is the wrong approach; so what should I do here?

I think that adding a \newline before 127 above would work, but as I said, I don't want to change this file directy.

Edit - Reproducing the error

Here is a sample to re-produce the error that I am getting, first you need the page "CreateSpace".

Then I am using this code to generate the file:

\documentclass{book}
\usepackage[size=novel,trim=0,paper=white,preview=false,gutter=0.5in,inner=0.25in,outer=0.25in,top=0.75in,bottom=0.75in,geometryextra={twoside,heightrounded,truedimen},colourpackage=xcolor,colorpackage=xcolor]{createspace}

\usepackage{index}
\usepackage{lipsum}
\usepackage{courier}

\makeatother
\makeindex
\begin{document}

\index{A}
\index{B}
\index{C}
\index{D}
\index{E}
\index{F}
\index{G}
\index{H}
\index{I}
\index{J}
\index{K}
\index{L}
\index{M}
\index{N}
\index{O}
\index{P}
\index{T}
\index{U}
\index{V}
\index{X}
\index{Y}
\index{A1}
\index{B2}
\index{C3}
\index{D4}
\index{E5}
\index{F6}
\index{G7}
\index{H8}
\index{I9}
\index{J10}
\index{K11}
\index{L12}
\index{M13}
\index{N14}
\index{O15}
\index{P16}
\index{T20}
\index{U21}
\index{V22}
\index{X23}
\index{Y24}

\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\index{Type!GetProperties()}
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\index{Type!GetProperties()}
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\index{Type!GetProperties()}
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\index{Type!GetProperties()}
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\index{Type!GetProperties()}
\lipsum[1-50]
\lipsum[1-50]
\lipsum[1-50]
\index{Type}
\index{Type!GetProperties()}

\printindex

\end{document}

After that I run: makeindex -s headings.ist MWE.idx

headings.ist contains the following:

headings_flag 1
heading_prefix "\\textbf\{\\large "
heading_suffix "\}"

If you now go to the end of the generated PDF, you will see that the index is out of the page margins:

Answer 1

You can first try relaxing the space parameters in the index:

\usepackage{etoolbox}
\appto{\theindex}{\spaceskip=.33333em plus .33333em minus .11111em }

This will allow the interword space to stretch a bit more (the usual stretching value is .22222em).

A different strategy might be

\usepackage{etoolbox}
\appto{\theindex}{\emergencystretch=6em }

which should result in a similar result.

The more drastic

\usepackage{etoolbox}
\appto{\theindex}{\sloppy}

is definitely not recommended.

Answer 2

An Index needs no justification. With the package ragged2e you can use the macro \RaggedRight to get a left-justified index. The ancillary effect of this: no overfull \hbox.

For example:

\documentclass[%
  a5paper      % papersize
 ,draft        % to show the overfull hbox
]{article}

\usepackage{index,lipsum,lmodern}
\usepackage{ragged2e}   % ragged margin with hyphenation
\makeindex

\begin{document}
\lipsum[1]\index{Type!GetProperties()}\clearpage\lipsum[1]\clearpage
\lipsum[1]\index{Type!GetProperties()}\clearpage\lipsum[1]\clearpage
\lipsum[1]\index{Type!GetProperties()}\clearpage\lipsum[1]\clearpage
\lipsum[1]\index{Type!GetProperties()}\clearpage\lipsum[1]\clearpage
\lipsum[1]\index{Type!GetProperties()}\clearpage\lipsum[1]\clearpage
\lipsum[1]\index{Type!GetProperties()}\clearpage\lipsum[1]\clearpage
\lipsum[1]\index{Type!GetProperties()}\clearpage
\index{Type}\index{Test}\index{Type!GetProperties()}

{              % start group
%\RaggedRight  % left-justified setting    % line 21
\printindex    % insert index here
}              % end group
\end{document}

You will get the warning "overfull hbox". With the class option draft the overfull box is marked with an black box. Delete the leading comment in line 21 and the warning disappears ...

My used index file is:

\begin{theindex}
{\bfseries\hfil T\hfil}\nopagebreak

  \item Test, 14
  \item Type, 14
    \subitem GetProperties(), 1, 3, 5, 7, 9, 11, 13, 14

\end{theindex}

My used ist file is:

% Index-Stildatei 
headings_flag    1  % Big letter before group
heading_prefix   "{\\bfseries\\hfil "
heading_suffix   "\\hfil}\\nopagebreak\n"
symhead_positive "Symbole"

delim_0  
delim_1  
delim_2