Field Definitions

http://msdn.microsoft.com/en-us/library/office/ms196289(v=office.15).aspx

<?xml version="1.0" encoding="utf-8"?>
<Elements xmlns="http://schemas.microsoft.com/sharepoint/">

  <Field ID="{1511BF28-A787-4061-B2E1-71F64CC93FD5}"
         Name="DateOpened"
         DisplayName="Date Opened"
         Type="DateTime"
         Format="DateOnly"
         Required="FALSE"
         Group="Financial Columns">
    <Default>[today]</Default>
  </Field>

  <Field ID="{060E50AC-E9C1-4D3C-B1F9-DE0BCAC300F6}"
         Name="Amount"
         DisplayName="Amount"
         Type="Currency"
         Decimals="2"
         Min="0"
         Required="FALSE"
         Group="Financial Columns" />

  <Field ID="{86811853-7E52-4515-A88D-A8FA9D450905}"
         Name="Client"
         DisplayName="Client Name"
         Type="Text"
         Required="FALSE"
         Group="Financial Columns"/>

  <Field ID="{943E7530-5E2B-4C02-8259-CCD93A9ECB18}"
         Name="CostCenter"
         DisplayName="Cost Center"
         Type="Choice"
         Required="FALSE"
         Group="Financial Columns">
    <CHOICES>
      <CHOICE>Administration</CHOICE>
      <CHOICE>Information</CHOICE>
      <CHOICE>Facilities</CHOICE>
      <CHOICE>Operations</CHOICE>
      <CHOICE>Sales</CHOICE>
      <CHOICE>Marketing</CHOICE>
    </CHOICES>
  </Field>
</Elements>

http://msdn.microsoft.com/en-us/library/office/aa979575(v=office.15).aspx

<Field
  Aggregation="sum" | "count" | "average" | "min" | "max" | "merge" | "plaintext" | "first" | "last"
  AllowDeletion="TRUE" | "FALSE"
  AllowDuplicateValues="TRUE" | "FALSE"
  AllowHyperlink="TRUE" | "FALSE"
  AllowMultiVote="TRUE" | "FALSE"
  AppendOnly="TRUE" | "FALSE"
  AuthoringInfo="Text"
  BaseType="Integer" | "Text"
  CalType="Integer"
  CanToggleHidden="TRUE" | "FALSE"
  ClassInfo="Text"
  ColName="Text"
  Commas="TRUE" | "FALSE"
  Customization=Text
  Decimals="Integer"
  DefaultListField="TRUE" | "FALSE"
  Description="Text"
  Dir="Text"
  DisplaceOnUpgrade="TRUE" | "FALSE"
  DisplayImage="Text"
  DisplayName="Text"
  DisplayNameSrcField="Text"
  DisplaySize=Integer
  Div="Number"
  EnableLookup="TRUE" | "FALSE"
  ExceptionImage="Text"
  FieldRef="Text"
  FillInChoice="TRUE" | "FALSE"
  Filterable="TRUE" | "FALSE"
  FilterableNoRecurrence="TRUE" | "FALSE"
  ForcedDisplay="Text"
  Format="DateOnly | DateTime | TimeOnly | EventList | ISO8601 | MonthDayOnly | MonthYearOnly | ISO8601Basic | ISO8601Gregorian | ISO8601BasicDateOnly | DropDown | RadioButtons | HyperLink | Image | TRUE | FALSE"
  FromBaseType="TRUE" | "FALSE"
  Group="Text"
  HeaderImage="Text"
  Height="Integer"
  Hidden="TRUE" | "FALSE"
  HTMLEncode="TRUE" | "FALSE"
  ID="Text"
  IMEMode="active | inactive"
  Indexed="TRUE" | "FALSE"
  IsolateStyles="TRUE" | "FALSE"
  IsRelationship="TRUE" | "FALSE"
  JoinColName="Text"
  JoinRowOrdinal="Integer"
  JoinType="INNER" | "LEFT OUTER" | "RIGHT OUTER"
  LCID="Integer"
  LinkToItem="TRUE" | "FALSE"
  List="Text"
  Max="Number"
  MaxLength="Integer"
  Min="Number" 
  Mult="TRUE" | "FALSE"
  Name="Text"
  NegativeFormat="MinusSign" | "Parens"
  Node="Text"
  NoEditFormBreak="TRUE" | "FALSE"
  NumLines="Integer"
  Overwrite="TRUE" | "FALSE"
  OverwriteInChildScopes="TRUE" | "FALSE"
  Percentage="TRUE" | "FALSE"
  PIAttribute="Text"
  PITarget="Text"
  PrependId="TRUE" | "FALSE"
  Presence="TRUE" | "FALSE"
  PrimaryKey="TRUE" | "FALSE"
  PrimaryPIAttribute="Text"
  PrimaryPITarget="Text"
  ReadOnly="TRUE" | "FALSE"
  ReadOnlyEnforced="TRUE" | "FALSE"
  RelationshipDeleteBehavior="Restrict | Cascade | None"
  RenderXMLUsingPattern="TRUE" | "FALSE"
  Required="TRUE" | "FALSE"
  RestrictedMode="TRUE" | "FALSE"
  ResultType="Text"
  RichText="TRUE" | "FALSE"
  RichTextMode="Text"
  RowOrdinal="Integer"
  Sealed="TRUE" | "FALSE"
  SeperateLine="TRUE" | "FALSE"
  SetAs="Text"
  ShowAddressBookButton="TRUE" | "FALSE"
  ShowField="Text" | "Choice" | "Counter"
  ShowInDisplayForm="TRUE" | "FALSE"
  ShowInEditForm="TRUE" | "FALSE"
  ShowInFileDlg="TRUE" | "FALSE"
  ShowInListSettings="TRUE" | "FALSE"
  ShowInNewForm="TRUE" | "FALSE"
  ShowInVersionHistory="TRUE" | "FALSE"
  ShowInViewForms="TRUE" | "FALSE"
  Sortable="TRUE" | "FALSE"
  SourceID="Text"
  StaticName="Text"
  StorageTZ="UTC" | "Abstract"
  StripWS="TRUE" | "FALSE"
  SuppressNameDisplay="TRUE" | "FALSE"
  TextOnly="TRUE" | "FALSE"
  Title="Text" 
  Type="Data_Type"
  UniqueId="Text"
  UnlimitedLengthInDocumentLibrary="TRUE" | "FALSE"
  URLEncode="TRUE" | "FALSE"
  URLEncodeAsUrl="TRUE" | "FALSE"
  UserSelectionMode="Text"
  UserSelectionScope="Integer"
  Viewable="TRUE" | "FALSE"
  Width="Integer"
  WikiLinking="TRUE" | "FALSE"
  XName="Text">
</Field>