7.49.3 Can you answer these questions?

7.49.3.1 Links in Reference List. DOI vs URL in `elsarticle-num.bst`

https://tex.stackexchange.com/landing/r/digest?cta=question&id=609824

A picture for context 
A few observations 
When doi field is defined in the .bib file, the bibliography style appends it very nicely at the end of the reference, as it can be seen in [3]. In addition, ... 
[bst]
 

asked by Eduardo Reis https://tex.stackexchange.com/landing/r/digest?cta=user&id=72983 1 vote

7.49.3.2 How formating chapter (no head), subsection with spaces and page number

https://tex.stackexchange.com/landing/r/digest?cta=question&id=610232

I am trying to format the chapter, section and subsection but I have not been able to. I have included an image as a reference of what I want to do. Here are some specifics: 
LaTeX, by default, puts ... 
[sectioning] [fancyhdr] [titlesec]
 

asked by royer https://tex.stackexchange.com/landing/r/digest?cta=user&id=167174 1 vote

answered by Pieter van Oostrum https://tex.stackexchange.com/landing/r/digest?cta=user&id=113546 0 votes

7.49.3.3 How to use the parameters? There is an @ symbol at the definition of \title

https://tex.stackexchange.com/landing/r/digest?cta=question&id=610376

What dose the symbol @ mean? 
@checktitle and s@title. 
How to use the two parameters? 
\renewcommand{\title}[2][]{% 
\gdef\@checktitle{#1}\ifx\@checktitle\empty\gdef\@title{#2} 
\gdef\s@title{#2}\else\... 
[titles]
 

asked by Blue Bird https://tex.stackexchange.com/landing/r/digest?cta=user&id=246678 1 vote