New line and no indent after \paragraph?

Question

I tried to use a \paragraph-environment, but I do want a new line after the title and no indent in the first textline.

New line is easy, but the first line is indented even if I use \noindent, \setlength{\parindent}{0pt} and \hangafter=0

I extracted an example:

\documentclass[12pt,a4paper,twoside]{scrreprt}

\usepackage[ngerman]{babel} 
\usepackage[T1]{fontenc}
\usepackage[latin9]{inputenc}
\usepackage{blindtext}

\setlength{\parindent}{0pt}
\hangafter=0

\begin{document}
    \subsection{subsection}
        \blindtext
    %\noindent %does not bring any effect
    \paragraph{paragraphNewline\newline}
        \blindtext
\end{document}

The first block is ok, but the second is not. I expect to try a \renewcommand / \renewenvironment, but I do not know what to write in.

In general: Is there an overview, where I can see the implementation of LaTeX-commands and -environments?

Answer 1

Since you asked, here's how you would redefine \paragraph:

\documentclass[12pt,a4paper,twoside]{scrreprt}

\usepackage[ngerman]{babel} 
\usepackage[T1]{fontenc}
\usepackage[latin9]{inputenc}
\usepackage{blindtext}

\makeatletter
\renewcommand\paragraph{\@startsection{paragraph}{4}{\z@}%
  {-3.25ex \@plus -1ex \@minus -0.2ex}%
  {0.01pt}%
  {\raggedsection\normalfont\sectfont\nobreak\size@paragraph}%
}
\makeatother

\begin{document}
    \subsection{subsection}
        \blindtext
    \paragraph{paragraph}
        \blindtext
\end{document}

The original definition is in your class file – here, scrreprt.cls. It uses the LaTeX command \@startsection, which is described in source2e. The 0.01pt is the amount of space to insert between the heading and text. As described in source2e, section ltsect.dtx, it must be above zero if you don't want a run-in head.

Answer 2

Instead of tweaking several different values and adding newlines manually, I would recommend setting parindent to zero in the documentclass parameters, and to use the titlesec package to give a paragraph heading the desired format.

\documentclass[parindent=0pt,12pt,a4paper,twoside]{scrreprt}

\usepackage[ngerman]{babel}
\usepackage[T1]{fontenc}
\usepackage[latin9]{inputenc}
\usepackage{blindtext}

\usepackage{titlesec}

\titleformat{\paragraph}
    {\normalfont\bfseries}
    {}
    {0pt}
    {}

\begin{document}
    \subsection{subsection}
        \blindtext
    \paragraph{paragraphNewline}
        \blindtext
\end{document}

See the titlesec documentation for a wealth of formatting options.