Yhyjyk

Problem Description

I am quite a newbie at *TeX, but I defined some newcommands as some kind of paragraph styles (maybe not the proper way to do so, maybe someone could tell me how to accomplish this better).

I want to have default paragraph style with no indentation, space after paragraph should be 0.08", space before paragraph should be 0". However, any of the paragraph style could change any of these settings and some something more (like character styles, e.g. bold, italics, underline, etc).

Now, sometimes I want to insert a paragraph in particular paragraph style without space after that paragraph. For that I use line break (\), which usually does the job. However, with the paragraphStyle below, this is broken.

It seems like if in the first paragraph, there is an indentation of a size of a space, which I cannot elimininate, no matter what I do.

What I have Tried

I tried to use noindent and setlengthparindent0em in many different combinations.

Minimal Working Example

%%%%% Preamble %%%%%
documentclass[10pt]book
usepackage[a4paper]geometry
geometry
 a4paper,
 left=1in,
 right=1in,
 top=1in,
 bottom=1in,
 portrait


usepackagexcolor

% Font family
usepackage[math-style=ISO, bold-style=ISO, partial=upright, nabla=upright]unicode-math
setmainfontLibertinus Serif

% Paragraph and line settings
setlengthparindent0em % Set paragraph indentation
setlengthparskip0.08in % Paragraph spacing
renewcommandbaselinestretch1.0 % Line expandafterselectlanguageexpandaftercvlang

% Custom commands
newcommandparagraphStyle[1]setlengthparindent0ptsetlengthparskip0.16inrenewcommandbaselinestretch2.0colorblack!100fontsize20pt24ptselectfonttextbf#1colorblack!100normalsizesetlengthparindent0emsetlengthparskip0.08inselectfontrenewcommandbaselinestretch1.0%

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

begindocument
 pagestyleempty

 This is wrong:

 paragraphStyle
 First line\
 Second line
 

 This is correct:

 paragraphStyleFirst line\
 paragraphStyleSecond line


 Also this is correct in indentation, but not in space after paragraph:

 First Line\
 Second Line
enddocument

Output

As Marcel pointed out, there is a stray space in your input. You can remove that space, as Marcel suggests, or you can add ignorespaces, within your macro definition, to your argument of textbf, prior to #1. Also, there is no need for the textbf to be in its own braces, so I removed it.

Note: an alternative for that part of the definition that now reads textbfignorespaces#1 could also be bfseries#1. Here, the braces are now necessary to limit the scope, but the ignorespaces is no longer required.

Also, I reorganized your definition of paragraphStyle to make it easier for humans to read. Note the presence of % end-of-line delimiters, to avoid the very same problem again.

documentclass[10pt]book
usepackage[a4paper]geometry
geometry
 a4paper,
 left=1in,
 right=1in,
 top=1in,
 bottom=1in,
 portrait


usepackagexcolor

% Font family
%usepackage[math-style=ISO, bold-style=ISO, partial=upright, nabla=upright]unicode-math
%setmainfontLibertinus Serif

% Paragraph and line settings
setlengthparindent0em % Set paragraph indentation
setlengthparskip0.08in % Paragraph spacing
renewcommandbaselinestretch1.0 % Line expandafterselectlanguageexpandaftercvlang

% Custom commands
newcommandparagraphStyle[1]%
 setlengthparindent0pt%
 setlengthparskip0.16in%
 renewcommandbaselinestretch2.0%
 colorblack!100%
 fontsize20pt24pt%
 selectfont%
 textbfignorespaces#1%
 colorblack!100%
 normalsize%
 setlengthparindent0em%
 setlengthparskip0.08in%
 selectfont%
 renewcommandbaselinestretch1.0%
%

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

begindocument
 pagestyleempty

 This is no longer wrong:

 paragraphStyle
 First line\
 Second line
 

 This is correct:

 paragraphStyleFirst line\
 paragraphStyleSecond line


 Also this is correct in indentation, but not in space after paragraph:

 First Line\
 Second Line
enddocument

The "indentation of a size of a space" actually isn't an indentation, it is a space at the start of the line:

Look at

 This is wrong:

 paragraphStyle
 First line\
 Second line
 

The newline after paragraphStyle{ is converted to a space which results in the observed "indentation".
You can avoid this by adding a % to comment the newline, suppressing the space:

 This is wrong:

 paragraphStyle%
 First line\
 Second line
 

The full document becomes

%%%%% Preamble %%%%%
documentclass[10pt]book
usepackage[a4paper]geometry
geometry
 a4paper,
 left=1in,
 right=1in,
 top=1in,
 bottom=1in,
 portrait


usepackagexcolor

% Font family
usepackage[math-style=ISO, bold-style=ISO, partial=upright, nabla=upright]unicode-math
setmainfontLibertinus Serif

% Paragraph and line settings
setlengthparindent0em % Set paragraph indentation
setlengthparskip0.08in % Paragraph spacing
renewcommandbaselinestretch1.0 % Line expandafterselectlanguageexpandaftercvlang

% Custom commands
newcommandparagraphStyle[1]setlengthparindent0ptsetlengthparskip0.16inrenewcommandbaselinestretch2.0colorblack!100fontsize20pt24ptselectfonttextbf#1colorblack!100normalsizesetlengthparindent0emsetlengthparskip0.08inselectfontrenewcommandbaselinestretch1.0%

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

begindocument
 pagestyleempty

 This is wrong:

 paragraphStyle%
 First line\
 Second line
 

 This is correct:

 paragraphStyleFirst line\
 paragraphStyleSecond line


 Also this is correct in indentation, but not in space after paragraph:

 First Line\
 Second Line
enddocument