display is fully defined in their own individual specifications; for example, the detail of what happens when display: flex is declared is defined in the CSS Flexible Box Model specification.
/ legacy values /
display: block;
display: inline;
display: inline-block;
display: flex;
display: inline-flex;
display: grid;
display: inline-grid;
display: flow-root;
/ box generation /
display: none;
display: contents;
/ two-value syntax /
display: block flow;
display: inline flow;
display: inline flow-root;
display: block flex;
display: inline flex;
display: block grid;
display: inline grid;
display: block flow-root;
/ other values /
display: table;
display: table-row; / all table elements have an equivalent CSS display value /
display: list-item;
/ Global values /
display: inherit;
display: initial;
display: revert;
display: unset;

display is fully defined in their own individual specifications; for example, the detail of what happens when display: flex is declared is defined in the CSS Flexible Box Model specification.

/* legacy values */
display: block;
display: inline;
display: inline-block;
display: flex;
display: inline-flex;
display: grid;
display: inline-grid;
display: flow-root;

/* box generation */
display: none;
display: contents;

/* two-value syntax */
display: block flow;
display: inline flow;
display: inline flow-root;
display: block flex;
display: inline flex;
display: block grid;
display: inline grid;
display: block flow-root;

/* other values */
display: table;
display: table-row; /* all table elements have an equivalent CSS display value */
display: list-item;

/* Global values */
display: inherit;
display: initial;
display: revert;
display: unset;

The CSS display property is specified using keyword values.