Pronouns
fbt:pronoun and fbt::pronoun both take a required FbtConstants::PRONOUN_USAGE enum and a Gender::GENDER_CONST enum:
class FbtConstants
{
    public const PRONOUN_USAGE = [
        "OBJECT" => 0,
        "POSSESSIVE" => 1,
        "REFLEXIVE" => 2,
        "SUBJECT" => 3
    ];
}
class Gender
{
    public const GENDER_CONST = [
        'NOT_A_PERSON' => 0,
        'FEMALE_SINGULAR' => 1,
        'MALE_SINGULAR' => 2,
        'FEMALE_SINGULAR_GUESS' => 3,
        'MALE_SINGULAR_GUESS' => 4,
        'MIXED_SINGULAR' => 5,
        'MIXED_PLURAL' => 5,
        'NEUTER_SINGULAR' => 6,
        'UNKNOWN_SINGULAR' => 7,
        'FEMALE_PLURAL' => 8,
        'MALE_PLURAL' => 9,
        'NEUTER_PLURAL' => 10,
        'UNKNOWN_PLURAL' => 11,
    ];
}
⚠️ NOTE: This is not the same gender as used in fbt:param, fbt:name, or subject!
The IntlVariations used in those cases only has GENDER_MALE, GENDER_FEMALE, and GENDER_UNKNOWN.
Pronoun example:
<fbt desc="pronoun example">
  <fbt:param name="name">{{ $ent->getName() }}</fbt:param>
  shared
  <fbt:pronoun type="possessive" gender="{{ $ent->getPronounGender() }}" />
  photo with you.
</fbt>
Optional attributes
- capitalize 
bool: Whether to capitalize the pronoun in the source string. - human 
bool: Whether to elide the NOT_A_PERSON option in the text variations generated. 
The example above generates:
{
  "hashToText": {
    "23fa7e4d6a4686bb6ff609c00726cf33": "{name} shared her photo with you.",
    "dd86ffccd845f2767c691f8d48f69e25": "{name} shared his photo with you.",
    "2584ed80718ca4138cd95adcf492de53": "{name} shared their photo with you."
  },
  ...,
  "type": "table",
  "desc": "pronoun example",
  "jsfbt": {
    "t": {
      "1": "{name} shared her photo with you.",
      "2": "{name} shared his photo with you.",
      "*": "{name} shared their photo with you."
    },
    "m": [
      null
    ]
  }
}
Combinations
Conceptually, pronouns work as though there was an enum supplied for the given type.
Below is the table of possible values for their various types.
Note how reflexive and object have 4 types
subject:    he/she/they
possessive: his/her/their
reflexive:  himself/herself/themselves/themself
object:     him/her/them/this
 V Name                  Subject Possessive Reflexive  Object
=============================================================
 0 NOT_A_PERSON          they    their      themself   this
 1 FEMALE_SINGULAR       she     her        herself    her
 2 MALE_SINGULAR         he      his        himself    him
 3 FEMALE_SINGULAR_GUESS she     her        herself    her
 4 MALE_SINGULAR_GUESS   he      his        himself    him
 5 MIXED_SINGULAR        they    their      themselves them
 5 MIXED_PLURAL          they    their      themselves them
 6 NEUTER_SINGULAR       they    their      themself   them
 7 UNKNOWN_SINGULAR      they    their      themself   them
 8 FEMALE_PLURAL         they    their      themselves them
 9 MALE_PLURAL           they    their      themselves them
10 NEUTER_PLURAL         they    their      themselves them
11 UNKNOWN_PLURAL        they    their      themselves them