[#appendix-tech-intro-theming]
= Theming

ifndef::snippets[:snippets: ../../../../../src/test/java/org/springframework/shell/docs]

Styling in a theming is provided by a use of a _AttributedString_ from `JLine`.
Unfortunately styling in `JLine` is mostly undocumented but we try to go through
some of its features here.

In `JLine` a style spec is a string having a special format. Spec can be given
multiple times if separated by a comma. A spec will either define a color for
foreground, background or its mode. Special format `<spec>:=<spec>` allows to
define a default within latter spec if former for some reason is invalid.

If spec contains a colon its former part indicates either foreground or background
and possible values are `foreground`, `fg`, `f`, `background`, `bg`, `b`, `foreground-rgb`,
`fg-rgb`, `f-rgb`, `background-rgb`, `bg-rgb` or `b-rgb`. Without rbg a color value
is name from an allowable colors `black`, `red`, `green`, `yellow`, `blue`, `magenta`,
`cyan` or `white`. Colors have their short formats `k`, `r`, `g`, `y`, `b`, `m`, `c` and `w`
respectively. If color is prefixed with either `!` or `bright-`, bright mode is automatically
applied. Prefixing with `~` will resolve from JLine internal bsd color table.

If rgb format is expected and prefixed with either `x` or `#` a normal
hex format is used.

[source, text]
----
fg-red
fg-r
fg-rgb:red
fg-rgb:xff3333
fg-rgb:#ff3333
----

If spec contains special names `default`, `bold`, `faint`, `italic`, `underline`, `blink`,
`inverse`, `inverse-neg`, `inverseneg`, `conceal`, `crossed-out`, `crossedout` or `hidden`
a style is changed accordingly with an existing color.

[source, text]
----
bold
bold,fg:red
----

If spec is a number or numbers separated with semicolon, format is a plain part of an ansi
ascii codes.

[source, text]
----
31
31;1
----

NOTE: JLine special mapping format which would resolve spec starting with dot can't be
used as we don't yet map those into Spring Shell styling names.