indentationparagraphs
Some weeks ago I've found here a thread about how to accomplish not indenting paragraphs when they consists on only one line. I can't find this thread now.
What I want is that \parindent only applies to paragraphs with two or more lines, the same as issuing \noindent before those one-liner paragraphs but in an automatic way.
The first line after the title of a sectional unit is not indented. If you want to change this behaviour, you could load the indentfirst package; i.e., write in the preamble:
\usepackage{indentfirst}
On a side note, the following line of your code
\renewcommand{\title}1{\raggedright{\textbf{\LARGE #1}\}}
will produce an error. Perhaps you meant something like
\renewcommand{\title}[1]{{\raggedright\LARGE\bfseries#1}}
Add listparindent=\parindent to the environment's optional argument.
\documentclass{article}
\usepackage{enumitem}
\begin{document}
\begin{description}[leftmargin=\parindent,topsep=0pt,partopsep=3pt,parsep=0pt,itemsep=3pt,
listparindent=\parindent]
\item[MY ITEM] Here is some text, and it is a paragraph. When it breaks
to the next line, it is indented.
This is my second paragraph. This result, however, does not indent
my second paragraph relative to the body text in the \verb|\item|.
\end{description}
\end{document}
Best Answer
If you're willing to wrap your document in a \vbox, the following seems to work. (So, this is only good for one page.)
"\prevgraf" is a primitive TeX integer variable that gives the number of lines in the last, or current, paragraph.
"\lastbox" is another primitive command that removes the last \vbox or \hbox on the current vertical or horizontal list and this box then becomes the \lastbox. It can't be used in vertical mode but can be used in internal vertical mode; hence the need to wrap things in a vbox.
I don't know if something similar, using \prevgraf, can be done in vertical mode.
The above was intended for Plain TeX, but it should work anywhere as it uses only primitive control sequences (I think).