"Features": named groups of settings

All delta options can go under the [delta] section in your git config file. However, you can also use named "features" to keep things organized: these are sections in git config like [delta "my-feature"]. Here's an example using two custom features:

[delta]
    features = unobtrusive-line-numbers decorations
    whitespace-error-style = 22 reverse

[delta "unobtrusive-line-numbers"]
    line-numbers = true
    line-numbers-minus-style = "#444444"
    line-numbers-zero-style = "#444444"
    line-numbers-plus-style = "#444444"
    line-numbers-left-format = "{nm:>4}┊"
    line-numbers-right-format = "{np:>4}│"
    line-numbers-left-style = blue
    line-numbers-right-style = blue

[delta "decorations"]
    commit-decoration-style = bold yellow box ul
    file-style = bold yellow ul
    file-decoration-style = none
    hunk-header-decoration-style = yellow box

The environment variable DELTA_FEATURES can used to enable features from the command line: it should be set to a space-separated string of feature names. If you precede this with a + symbol, then the features are added to those configured elsewhere, instead of replacing them. This is very useful, for example to temporarily switch delta to side-by-side mode you can do

export DELTA_FEATURES=+side-by-side

and to undo that:

export DELTA_FEATURES=+