The Example "Diagrams as Simple Graphs" from LaTeX TikZ Documentation

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\documentclass[border=20pt,tikz]{standalone}
\usepackage{xcolor}
\usepackage{tikz}
\usetikzlibrary{shapes.misc,graphs,arrows.meta}

\begin{document}

\begin{tikzpicture}
[ % The graphic options are specified in key lists. All graphic options are local to the `{tikzpicture}` to which they apply.
>={Stealth[round]}, % Arrow style; `>` stands for the end of the arrow, equal to `<->/.tip`
black!50, % Arrow color
text=black, % Text color
thick, % Arrow weight
every new ->/.style = {shorten >=1pt}, 
% `every new ->` means that "whenever encountering ->"
% `shorten >=1pt` means that "shorten the path by 1pt in the direction of the end point."
% Note that there should be one or more space after the `shorten` key, otherwise an error will occur
graphs/every graph/.style = {edges=rounded corners},
% Specify all edges in the graph, i.e., connections between nodes, be drawn with rounded corners
% `graphs` is a TikZ package
skip loop/.style = {to path = {-- ++(0,#1) -| (\tikztotarget)}}, % Define a new style called `skip loop`
hv path/.style = {to path = {-| (\tikztotarget)}}, % Define a new style called `hv path` 
vh path/.style = {to path = {|- (\tikztotarget)}}, % Define a new style called `vh path`
nonterminal/.style = { % Define a new style called `nonterminal`
	rectangle,
	minimum size = 6mm,
	very thick,
	draw = red!50!black!50,
	top color = white,
	bottom color = red!50!black!20,
	font = \itshape,
	text height = 1.5ex,
	text depth = .25ex},
terminal/.style = { % Define a new style called `terminal`
	rounded rectangle,
	minimum size = 6mm,
	very thick,
	draw=black!50,
	top color = white,
	bottom color = black!20,
	font = \ttfamily,
	text height = 1.5ex,
	text depth = .25ex},
shape = coordinate % Comment this line to see the "name" of p1, p2, p3 etc.
]

\graph [grow right sep, branch down=7mm, simple]
{
	/ -> unsigned integer [nonterminal] -- p1 -> "." [terminal] -- p2 -> digit [terminal] -- p3 -- p4 -- p5 -- E [terminal] -- q1 -> 
	[vh path] {[nodes = {yshift=7mm}] "+" [terminal], q2, "-" [terminal]} -> 
	[hv path] q3 -- ui2/unsigned integer [nonterminal] -- p6 -> /;
	% Because "unsigned integer" is node content and simultaneously node name and we use it twice,
	% we should assign a new node name for the second one, i.e., "ui2" in "ui2/unsigned integer", to make a distinction.
	% On the other hand, due to that we won't use this node name later, we can write nothing before /, i.e., `/unsigned integer`,
	% which stands for a "fresh, anonymous" node name.
	
	p1 -> [skip loop = 5mm] p4;
	p3 -> [skip loop = -5mm] p2;
	p5 -> [skip loop = -11mm] p6;
	
	q1 -- q2 -- q3;
};
\end{tikzpicture}

\end{document}

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\documentclass[border=20pt,tikz]{standalone}
\usepackage{xcolor}
\usepackage{tikz}
\usetikzlibrary{graphs,arrows.meta}

\begin{document}

\begin{tikzpicture}
[
>={Stealth[round]},
thick,black!50,
text=black,
every new ->/.style = {shorten >=1pt},
graphs/every graph/.style = {edges=rounded corners},
node distance = 5mm and 5mm,
text height = 1.5ex,
text depth = .25ex,
nonterminal/.style = { % Define a new style called `nonterminal`
	rectangle,
	minimum size = 6mm,
	very thick,
	draw = red!50!black!50,
	top color = white,
	bottom color = red!50!black!20,
	font=\itshape},
terminal/.style = { % Define a new style called `terminal`
	rectangle,
	minimum size = 6mm,
	very thick,
	draw = black!50,
	top color = white,
	bottom color=black!20,
	font=\ttfamily,
	rounded corners = 3mm},
point/.style = { % Define a new style called `point`
	coordinate,
	% circle,
	% inner sep = 0pt,
	% minimum size = 1pt,
	% fill = red
	},
skip loop/.style = {to path={-- ++(0,#1) -| (\tikztotarget)}}, % Define a new style called `skip loop`
hv path/.style = {to path = {-| (\tikztotarget)}}, % Define a new style called `hv path`
vh path/.style = {to path = {|- (\tikztotarget)}} % Define a new style called `vh path`
]

% Use TikZ matrix to align quite arbitrary graphical objects in rows and columns
\matrix[row sep = 1mm, column sep = 4mm]{
	% First row:
	& & & & & & & & & & & (plus) \node (plus) [terminal] {+};\\
	% Second row:
	\node (p1) [point] {}; & \node (ui1) [nonterminal] {unsigned interger}; &
	\node (p2) [point] {}; & \node (dot) [terminal] {.}; &
	\node (p3) [point] {}; & \node (digit) [terminal] {digit}; &
	\node (p4) [point] {}; & \node (p5) [point] {}; &
	\node (p6) [point] {}; & \node (e) [terminal] {E}; &
	\node (p7) [point] {}; & &
	\node (p8) [point] {}; & \node (ui2) [nonterminal] {unsigned interger}; &
	\node (p9) [point] {}; & \node (p10) [point] {};\\
	% Third row:
	& & & & & & & & & & & \node (minus) [terminal] {-};\\
};

\graph[use existing nodes] {
	(p1) -> (ui1) -- (p2) -> (dot) -- (p3) -> (digit) -- (p4)
	     -- (p5) -- (p6) -> (e) -- (p7) -- (p8) -> (ui2) -- (p9) -> (p10);
	(p4) -> [skip loop = -5mm] (p3);
	(p2) -> [skip loop = 5mm] (p5);
	(p6) -> [skip loop = -11mm] (p9);
	(p7) -> [vh path] (plus) -> [hv path] (p8);
	(p7) -> [vh path] (minus) -> [hv path] (p8);
};
\end{tikzpicture}

\end{document}